This review deals with the largest set of rat recombinant inbred (RI) strains and summarizes past and recent accomplishments with this platform for genetic mapping and analyses of divergent and complex traits. This strain, derived by crossing the spontaneously hypertensive rat, SHR/Ola, with a Brown Norway congenic, BN-Lx, carrying polydactyly-luxate syndrome, is referred to as HXB/BXH. The RI strain set has been used for linkage and association studies to identify quantitative trait loci for numerous cardiovascular phenotypes, including arterial pressure, stress-elicited heart rate, and pressor response, and metabolic traits, including insulin resistance, dyslipidemia and glucose handling, and left ventricular hypertrophy. The strain's utility has been enhanced with development of a new framework marker-based map and strain distribution patterns of polymorphic markers. Quantitative trait loci for behavioral traits mapped include loci for startle motor response and habituation, anxiety and locomotion traits associated with elevated plus maze, and conditioned taste aversion. The polydactyly-luxate syndrome Lx mutation has allowed the study of alleles important to limb development and malformation phenotypes as well as teratogens. The RI strains have guided development of numerous congenic strains to test locus assignments and to study the effect of genetic background. Although these strains were originally developed to aid in studies of rat genetic hypertension and morphogenetic abnormalities, this rodent platform has been shown to be equally powerful for a wide spectrum of traits and endophenotypes. These strains provide a ready and available vehicle for many physiological and pharmacological studies.

Alemayehu, Adamu, Laura Breen, Drahomira Krenova, and Morton P. Printz. Reciprocal rat chromosome 2 congenic strains reveal contrasting blood pressure and heart rate QTL. Physiol Genomics 10: 199-210, 2002. First published July 23, 2002 10.1152/physiolgenomics.00065.2002.-Evidence exists implying multiple blood pressure quantitative trait loci (QTL) on rat chromosome 2. To examine this possibility, four congenic strains and nine substrains were developed with varying size chromosome segments introgressed from the spontaneously hypertensive rat (SHR/lj) and normotensive Wistar-Kyoto rat (WKY/lj) onto the reciprocal genetic background. Cardiovascular phenotyping was conducted with telemetry over extended periods during standard salt (0.7%) and high-salt (8%) diets. Our results are consistent with at least three independent pressor QTL: transfer of SHR/lj alleles to WKY/lj reveals pressor QTL within D2Rat21-D2Rat27 and D2Mgh10-D2Rat62, whereas transfer of WKY/lj D2Rat161-D2Mit8 to SHR/lj reveals a depressor locus. Our results also suggest a depressor QTL in SHR/lj located within D2Rat161-D2Mgh10. Introgressed WKY/lj segments also reveal a heart rate QTL within D2Rat40-D2Rat50 which abolished salt-induced bradycardia, dependent upon adjoining SHR/lj alleles. This study confirms the presence of multiple blood pressure QTL on chromosome 2. Taken together with our other studies, we conclude that rat chromosome 2 is rich in alleles for cardiovascular and behavioral traits and for coordinated coupling between behavior and cardiovascular responses. hypertension; genetic; salt; SHR; telemetry PUTATIVE ARTERIAL PRESSURE loci have been identified on over half of the chromosomes of the spontaneously hypertensive rat (SHR) and on numerous chromosomes of the Dahl salt-sensitive (Dahl-S) hypertensive rat (5,16,17,21). However, when individual loci are separated out and expressed on a uniform homozygous genetic background, as in congenics or consomics, their individual contributions to elevated arterial pressure sums to greater than 100% of the total observed hypertension in the original genetic model. This finding likely implies 1) a modifying influence of the heterozygous genetic background, 2)

1The effects of the inhibitor of nitric oxide (NO) synthesis, N0-nitro-L-arginine methyl ester (L-NAME), on systemic arteriil blood pressure and jejunal motility, blood flow, and oxygen uptake have been investigated in anaesthetized dogs. 2 L-NAME (cumulative doses of 0.1-20 mg kg-', i.v.) dose-dependently increased blood pressure and jejunal motility and decreased heart rate. The maximal response of these three variables occurred at doses, 3, 10 and 10mgkg-l, respectively. L-NAME (cumulative doses of 0.5-5mgkg-') also dosedependently induced jejunal vasoconstriction. The jejunal vascular resistance returned to control values as the cumulative doses reached 10 and 20 mg kg-', which corresponded to the maximal increase in jejunal motility. 3 A single intravenous injection of L-NAME (10mgkg-') produced a prompt increase in blood pressure, which lasted for at least 50min. 4 L-NAME (10 mg kg-') produced a progressive rise in jejunal motility reaching its maximum (47 ± 6 mmHg) 15 min after the administration, and lasting for 40-50 min. Both the basal lumen pressure and the amplitude of rhythmic contractions increased during this period. 5 L-NAME (10 mg kg-') produced a triphasic change in jejunal vascular resistance and blood flow measured by timed collection of venous outflow. The blood flow decreased initially (-43% at 5 min), increased (+ 35%) and returned to control value between 15 and 35 min, then decreased (-35%) 40-50 min post-infusion. Jejunal vascular resistance reflected the blood flow response (+ 88% at both 5 and 50 min). The time during which the reversal of the vasoconstriction occurred (15-35 min) corresponded to the time of marked increase in motility, and was accompanied by a significant increase in jejunal oxygen uptake (+ 18%). 6 The L-NAME-induced increase in motility was prevented by L-arginine (1 g kg-', i.v.) but not by D-arginine pretreatment. The interim (15-35 min) changes in jejunal blood flow, vascular resistance and oxygen uptake were also prevented by L-arginine pretreatment. 7 L-Arginine pretreatment attenuated L-NAME-induced hypertension for 5 min. 8 The L-NAME-induced increases in jejunal vascular resistance and motility were inhibited by either local intra-arterial infusion of L-arginine (32 mM local arterial blood concentration) or topical application of 2 gM nitroglycerin. Infusion of D-arginine (32 mM local arterial blood concentration) had no such effect. 9 The L-NAME-induced increase in blood pressure was not the mechanism by which jejunal motility was increased, because similar increases in blood pressure by mefenamate (10 mg kg-', i.v.) had no such effect. 10 Thus, inhibition of nitric oxide synthesis by L-NAME increased jejunal motility and vascular resistance and the marked increase in motility can abolish or reverse the vasoconstriction. Endogenous nitric oxide may play a role in regulating motility and blood flow in the resting canine jejunum.

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The role of prostanoids in regulation of jejunal blood flow (JBF) was studied in anesthetized dogs. Intra-arterial infusions of arachidonate produced biphasic changes and dose-dependent decreases in jejunal vascular resistance (JVR) in untreated and aspirin-pretreated dogs, respectively; mefenamate abolished these responses. The jejunum released prostaglandin I2 (PGI2) greater than PGE2 greater than thromboxane A2 (TXA2) (radioimmunoassay) under resting conditions, and food enhanced the release of PGE2 greater than PGI2 greater than TXA2 greater than PGF2 alpha. Addition of arachidonate to food enhanced TXA2 and PGF2 alpha releases and decreased PGI2 and PGE2 releases, while inhibiting the food-induced increases in JBF and O2 uptake; mefenamate inhibited these arachidonate actions. A TXA2 receptor antagonist (SQ-29548) reversed the arachidonate vascular and metabolic actions. Intra-arterial infusions of PGI2 or PGE2 decreased, whereas TXA2 analogue U-44069 or PGF2 alpha increased JVR. A mixture of these prostanoids infused at blood concentrations similar to the increase observed during food placement did not alter JVR. At concentrations similar to the increases observed when arachidonate was added to luminal food, the infusions increased JVR and abolished the food-induced decrease in JVR. In conclusion, jejunal productions of PGI2, PGE2, TXA2, and PGF2 alpha increase during nutrient absorption. Addition of arachidonate to food attenuates the former two and enhances the latter two releases, which act to attenuate food-induced jejunal hyperemia.

Spontaneously hypertensive rats (SHR) exhibit enhanced pressor, heart rate, and nociceptive responses to spinal nicotinic agonists. This accompanies a paradoxical decrease in spinal nicotinic receptor number in SHR compared with normotensive rats. The congenic strain, SHR-Lx, with an introgressed chromosome 8 segment from the normotensive Brown-Norway-Lx strain (BN-Lx) exhibits reduced blood pressure. This segment contains a gene cluster for three nicotinic receptor subunits expressed in the nervous system. We examined the implication of this gene cluster in the enhanced responsiveness of the SHR. Pressor and nociceptive responses to spinal cytisine, a nicotinic agonist, were diminished in SHR-Lx. Moreover, with repeated administration, these responses desensitized faster in SHR-Lx and progenitor BN-Lx than in progenitor SHR/Ola. This implicates the gene cluster in both cardiovascular and nociceptive responses to spinal nicotinic agonists. Since diminished responsiveness to agonist stimulation is greater than the basal blood pressure differences between the strains and the introgressed rat chromosome maps to a quantitative trait locus in human hypertension, polymorphisms in the three nicotinic receptor genes become candidates for altered central control of blood pressure.

Alemayehu, Adamu, Laura Breen, and Morton P. Printz. A new inbred Wistar-Kyoto rat substrain exhibiting apparent salt sensitivity and borderline hypertension. Am J Physiol Heart Circ Physiol 283: H1181-H1190, 2002. First published May 23, 2002 10.1152/ajpheart.00187.2002The normotensive Wistar-Kyoto (WKY) rat strain is a traditional control for the spontaneously hypertensive rat (SHR). We found trait differences between two inbred normotensive WKY strains, derived originally from different vendors, and compared these two strains from La Jolla-Taconic Farms (WKY/lj-tf) and La Jolla-Charles River (WKY/lj-cr) with the inbred SHR/lj-cr for cardiovascular, diurnal, and activity traits under normal and high (8%) NaCl diets. Marked genetic diversity was found between the two vendor-derived WKY. By using an extended study design and radiotelemetry, we compared WKY/lj-cr, WKY/lj-tf, and SHR/lj-cr with the following results: systolic pressure (120 Ϯ 1, 133 Ϯ 1, 168 Ϯ 3 mmHg, respectively); diurnal variation in heart rate (⌬HR: 46 Ϯ 3, 71 Ϯ 4, 57 Ϯ 2 beats/min, respectively); and salt sensitivity of arterial pressure (⌬systolic: 10 Ϯ 1, 21 Ϯ 1, 20 Ϯ 1 mmHg, respectively). The WKY/lj-tf genotype apparently results in compromised control of arterial pressure and heart rate, especially during high NaCl intake, and greater susceptibility to high pressure (i.e., high NaCl-induced secondary changes). WKY/lj-tf thus constitutes a new inbred borderline hypertensive WKY substrain offering unique opportunities for genomic studies into the development of genetic hypertension. inbred strains; hypertension sodium-dependent; genotype; circadian rhythm; radiotelemetry; heart rate; polymorphism MOST INVESTIGATORS have been using descendants of the normotensive Wistar-Kyoto (WKY) rat strain as the control for the Okamoto and Aoki (20) spontaneously hypertensive rat (SHR). As a result of both highly inbred original stock and standardized breeding practices, virtual uniformity has resulted in the SHR supplied by major commercial vendors (5). However, the rigorous procedures applied to the initial inbreeding and subsequent distribution of the SHR were not used for the WKY rat derived after the SHR. As a result, animals were distributed to commercial suppliers as early as the 10th generation of inbreeding (13). Furthermore, subsequent breeding was not standardized with some suppliers (including Charles River Laboratories) maintaining brother-sister matings (10) to sustain the founder stock, whereas others (including Taconic Farms) used a random breeding (outbred) protocol (26).Studies from several laboratories, including our own, compared WKY rats from Charles River Laboratories (WKY/cr; Wilmington, MA) and Taconic Farms (WKY/ tf; Germantown, NY) and reported pronounced trait differences (9,13,14,24). Our own laboratory (8), as early as 1984, noted differences in 1) consummatory behaviors including an enhanced salt preference in WKY/tf, 2) age-weight relationships, and 3) cardiovascular traits between these WKY substrains. Furthermore, we rep...

The effects of a thromboxane A2 (TxA2)-endoperoxide receptor antagonist, SQ 29548, on jejunal blood flow, oxygen uptake, and capillary filtration coefficient (Kfc) were determined in anesthetized dogs under resting conditions and during the presence of predigested food in the jejunal lumen in three series of experiments. In series 1, 2.0 micrograms intra-arterial administration of SQ 29548 was found to abolish completely the vasoconstrictor action of graded doses (0.05-2.0 micrograms) of intra-arterial injection of a TxA2-endoperoxide analogue, U44069. SQ 29548 (2.0 micrograms ia) per se did not significantly alter resting jejunal blood flow, oxygen uptake, capillary pressure, or Kfc. Before SQ 29548, placement of food plus bile into the jejunal lumen increased blood flow +42 +/- 9%, oxygen uptake +28 +/- 7%, and Kfc +24 +/- 6%. After SQ 29548, the food placement increased blood flow +37 +/- 8%, oxygen uptake +52 +/- 11%, and Kfc +63 +/- 20%. The food-induced increases in oxygen uptake and Kfc after SQ 29548 were significantly greater than those induced before the blocking of TxA2-endoperoxide receptors by SQ 29548. Our study indicates that endogenous thromboxane does not play a role in regulating jejunal blood flow, capillary filtration, and oxygen uptake under resting conditions. However, it plays a role in limiting the food-induced increases in jejunal oxygen uptake and capillary exchange capacity without influencing the food-induced hyperemia.