No abstract

The present study evaluated the possible changes in the autonomic control of heart rate in the hypertensive model induced by the inhibition of nitric oxide synthase. Rats were treated with N(G)-nitro-L-arginine methyl ester (L-NAME group) in the drinking water during 7 days, whereas control groups were treated with tap water (control group) or with the N(G)-nitro-D-arginine methyl ester (D-NAME group), an inactive isomer of the L-NAME molecule. The L-NAME group developed hypertension and tachycardia. The sequential blockade of the autonomic influences with propranolol and methylatropine indicated that the intrinsic heart rate did not differ among groups and revealed a sympathetic overactivity in the control of heart rate in the L-NAME group. The spectral density power of heart rate, calculated using fast-Fourier transformation, indicated a reduced variability in the low-frequency band (0.20-0.60 Hz) for the L-NAME group. The baroreflex sensitivity was also attenuated in these animals when compared with the normotensive control or D-NAME group. Overall, these data indicate cardiac sympathetic overactivity associated with a decreased baroreflex sensitivity in L-NAME hypertensive rats.

In conscious chronic (12 to 18 weeks) streptozotocin diabetic rats, we examined the changes in basal heart rate, with particular attention to heart rate variability assessed by evaluating the standard deviation (bpm) of the lengths of adjacent pulse pressure. We also investigated in anesthetized rats the ability of the aortic baroreceptors to acutely (30 minutes) reset to hypertensive levels. For this purpose, pressure-nerve activity curves for the baroreceptors were obtained, and gain (slope of the curve) and mean arterial pressure at 50% of maximal baroreceptor activity were calculated. The shift of the pressure-nerve activity curve was used as an index of resetting. Conscious diabetic rats (n=6) exhibited lower mean arterial pressure (93+/-6 versus 109+/-4 mm Hg), heart rate (272+/-25 versus 359+/-11 bpm), and heart rate variability (18+/-7 versus 36+/-6 bpm) than control rats (n=7). Under anesthesia, diabetic rats (n=7) and control rats (n=8) exhibited similar mean arterial pressure (113+/-6 versus 109+/-7 mm Hg in control rats ), mean arterial pressure at 50% of maximal baroreceptor activity (117+/-5 versus 107+/-6 bpm), gain (1.66+/-0.08 versus 1.81+/-0.05%/mm Hg), and extent of resetting (44+/-12 versus 49+/-9%) to hypertensive levels. The present study demonstrated that conscious chronic diabetic rats presented lower heart rate variability than control rats. On the other hand, chronic diabetes was not associated with alterations in baroreceptor function or its ability to rapidly reset to hypertensive levels.

A partial cDNA which encodes the rat homolog of human placental protein-12, the low mol wt insulin-like growth factor-binding protein (IGFBP-1), has been isolated from a rat decidual cDNA library using low stringency hybridization with a human IGFBP-1 cDNA probe. The incomplete cDNA obtained from this library was used to screen a rat liver cDNA library from which a full-length cDNA was obtained. The predicted amino acid sequence of rat IGFBP-1 showed 66%, 29%, and 34% sequence identity with the human IGFBP-1, the human GH-dependent binding protein IGFBP-3, and rat IGFBP-2, the BP secreted by buffalo rat liver cells, respectively. The rat IGFBP-1 cDNA hybridized with a 1.6-kilobase transcript which was easily detected in uterine RNA from the pseudopregnant rat and RNA from the liver and kidney of adult rats. A low level of expression was apparent in the brain and the diestrous uterus. Of the tissues examined the order of abundance of IGFBP-1 mRNA was deciduoma tissue greater than or equal to liver much greater than kidney much greater than uterus greater than brain. The 1.6-kb mRNA was more abundant in RNA from neonatal rat liver than in that from maternal liver, but was not detected in total RNA (50 micrograms) from other neonatal rat tissues (kidney, lung, brain, and heart). Under stringent conditions, rat IGFBP-1 did not hybridize with RNA from the BRL-3A rat liver cell line. In food-deprived rats, hepatic IGFBP-1 mRNA was increased 10.0 +/- 2.2-fold compared to that in control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Our findings that the mid-frequency band variability of arterial pressure was reduced in diabetic patients suggest that sympathetic modulation of the cardiovascular system is impaired, corroborating other studies in such patients using this and other approaches.