One of the postulated main luteolytic actions of prostaglandin (PG) F(2 alpha) is to decrease ovarian blood flow. However, before Day 5 of the normal cycle, the corpus luteum (CL) is refractory to the luteolytic action of PGF(2 alpha). Therefore, we aimed to determine in detail the real-time changes in intraluteal blood flow after PGF(2 alpha) injection at the early and middle stages of the estrous cycle in the cow. Normally cycling cows at Day 4 (early CL, n = 5) or Days 10--12 (mid CL, n = 5) of the estrous cycle (estrus = Day 0) were examined by transrectal color and pulsed Doppler ultrasonography to determine the blood flow area, the time-averaged maximum velocity (TAMXV), and the volume of the CL after an i.m. injection of a PGF(2 alpha) analogue. Ultrasonographic examinations were carried out just before PG injection (0 h) and then at 0.5, 1, 2, 4, 8, 12, 24, and 48 h after the injection. Blood samples were collected at each of these times for progesterone (P) determination. The ratio of the colored area to a sectional plane at the maximum diameter of the CL was used as a quantitative index of the changes in blood flow within the luteal tissue. Blood flow within the midcycle CL initially increased (P < 0.05) at 0.5-2 h, decreased at 4 h to the same levels observed at 0 h, and then further decreased to a lower level from 8 h (P < 0.05) to 48 h (P < 0.001). Plasma P concentrations decreased (P < 0.05) from 4.7 +/- 0.5 ng/ml (0 h) to 0.6 +/- 0.2 ng/ml (24 h). The TAMXV and CL volume decreased at 8 h (P < 0.05) and further decreased (P < 0.001) from 12 to 24 h after PG injection, indicating structural luteolysis. These changes were not detected in the early CL, in which luteolysis did not occur. In the early CL, the blood flow gradually increased in parallel with the CL volume, plasma P concentration, and TAMXV from Day 4 to Day 6. The present results indicate that PGF(2 alpha) induces an acute blood flow increase followed by a decrease in the midcycle CL but not in the early CL. This transitory increase may trigger the luteolytic cascade. The lack of intraluteal vascular response to PG injection in the early CL appears to be directly correlated with the ability to be resistant to PG.

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Holstein cattle dominate the global milk production industry because of their outstanding milk production, however, this breed is susceptible to tropical endemic pathogens and suffers from heat stress and thus fewer Holstein populations are raised in tropical areas. The bovine major histocompatibility complex (BoLA)-DRB3 class II gene is used as a marker for disease and immunological traits, and its polymorphism has been studied extensively in Holstein cattle from temperate and cold regions. We studied the genetic diversity of the BoLA-DRB3 gene in South American Holstein populations to determine whether tropical populations have diverged from those bred in temperate and cold regions by selection and/or crossbreeding with local native breeds. We specifically studied Exon 2 of this gene from 855 South American Holstein individuals by a polymerase chain reaction (PCR) sequence-based typing method. We found a high degree of gene diversity at the allelic (Na > 20 and He > 0.87) and molecular (π > 0.080) levels, but a low degree of population structure (FST = 0.009215). A principal components analysis and tree showed that the Bolivian subtropical population had the largest genetic divergence compared with Holsteins bred in temperate or cold regions, and that this population was closely related to Bolivian Creole cattle. Our results suggest that Holstein genetic divergence can be explained by selection and/or gene introgression from local germplasms. This is the first examination of BoLA-DRB3 in Holsteins adapted to tropical environments, and contributes to an ongoing effort to catalog bovine MHC allele frequencies by breed and location.

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Abstract. The objective of the present study was to investigate the influence of prostaglandin F2α (PGF2α) and nitric oxide (NO) on production of steroids and PGs by culturing bovine luteal cells obtained from ovaries on days 8-12 of the estrous cycle with a nitric oxide (NO) donor (Spermine NONOate), and a NO synthase inhibitor (N G -nitro-L-arginine methyl ester dihydrochloride: L-NAME). When the cells were exposed for 24 h to PGF2α (10 -7 -10 -5 M), production of progesterone (P4) increased significantly at all doses used (P<0.05). Moreover, PGF2α stimulated PGF2α production (P<0.01), depressed testosterone (T) production (P<0.05), but did not affect synthesis of prostaglandin E2 (PGE2). Spermine NONOate decreased P4 production to 66%, 47% and 34% of the control concentration after treatment with 10 -5 M, 10 -4 M and 10 -3 M, respectively, but did not affect T production, and increased PGF2α synthesis (P<0.05) and PGE2 (P<0.01) at all doses used. L-NAME increased production of P4 (P<0.01) but did not affect (P>0.05) secretion of T, PGF2α and PGE2. Estradiol-17β (E2) was detectable on the level of sensitivity of assay and was not significantly altered by any treatments. The overall results suggest that PGF2α and NO produced locally in bovine CL play roles in the regulation of the secretory function of the bovine CL as auto/paracrine factors. Key words: Prostaglandins, Progesterone, Nitric oxide, Corpus luteum, Cow (J. Reprod. Dev. 50: [411][412][413][414][415][416][417] 2004) he function of the bovine corpus luteum (CL) is responds to many intra-and extraluteal factors [1,2]. It has been well documented that injections of prostaglandin F 2 α , (PGF 2 α ) analogues in ruminants decrease progesterone (P 4 ) production, consequently shortening the estrous cycle [2]. However, a number of in vitro studies indicate that PGF 2α does not have a direct, luteolytic influence on the bovine steroidogenic luteal cells [3,4]. It has been suggested that some substances produced locally in the bovine CL by steroidogenic as well as non-steroidogenic cells mediate the luteolytic action of PGF 2α . We found that nitric oxide (NO) is locally produced in the bovine CL during the estrous cycle with higher levels during the late luteal phase [5]. Moreover, the effects of PGF 2α were inhibited by an inhibitor of NO synthase (NOS), suggesting that NO is a potent mediator of the luteolytic action of PGF 2α in vivo [5][6][7].Recent studies have demonstrated that NO also regulates P4 and PG production in the bovine CL

To determine whether glucocorticoids (GCs) play a role in regulating uterine function in cow, the present study examined the expression of mRNA encoding GC receptor (GC-R) a, 11b-hydroxysteroid dehydrogenase (11-HSD) type 1 and type 2, and the activity of 11-HSD1 in bovine endometrial tissue throughout the estrous cycle. We also studied the effects of cortisol on basal, oxytocin (OT)-and tumor necrosis factor-a (TNFa)-stimulated prostaglandin (PG) production. A quantitative real-time PCR analysis revealed that GC-Ra mRNA was expressed more strongly in the mid-luteal stage (days 8-12) than in the other stages. In contrast to GC-Ra mRNA expression, 11-HSD1 mRNA expression was greater in the follicular stage than in the other stages, whereas 11-HSD2 mRNA expression was lowest in the follicular stage. The activity of 11-HSD1 was greater in the follicular stage and estrus than in the other stages and was lowest in the mid-luteal stage. Cortisone was dosedependently converted to cortisol in the cultured endometrial tissue. Although cortisol did not affect either the basal or OT-stimulated production of PGs in the cultured epithelial cells, the production of PGs stimulated by TNFa in the stromal cells was suppressed by cortisol (P!0 . 05). Cortisol suppressed basal prostaglandin (PG)F2a without affecting basal PGE2 production in the stromal cells. The overall results suggest that the level of cortisol is locally regulated in bovine endometrium throughout the estrous cycle by 11-HSD1, and that cortisol could act as a luteoprotective factor by selectively suppressing luteolytic PGF2a production in bovine endometrium.

Oxygen deficiency caused by a decrease in the blood supply is known to induce various responses of cells. Because luteal blood flow has been shown to decrease during luteolysis, a low-oxygen condition seems to be an integral part of the environment during luteolysis. To determine whether a low-oxygen condition is associated with functional luteolysis, we examined the influence of reduced oxygen tension on the luteal progesterone (P4) generating system in cultured bovine midluteal cells. Luteal cells obtained from midcycle corpus luteum (d 8-12) were incubated under different O2 concentrations (20, 10, 5, 3% O2) with or without LH for 24 h. P4 production decreased with decreasing O2 concentration but was significantly stimulated by LH regardless of O2 concentration. After 8 h of culture, both basal and LH-stimulated P4 production was significantly lower under 3% O2 than under 20% O2. Low-oxygen condition also inhibited pregnenolone production. Cytochrome P450 side-chain cleavage enzyme (P450scc) mRNA expression, measured by quantitative PCR, decreased under low-oxygen condition in both non-LH-treated and LH-treated cells. Low-oxygen condition did not affect the expressions of steroidogenic acute regulatory protein mRNA or protein, whereas steroidogenic acute regulatory protein mRNA expression was stimulated by LH during 4 h of culture. Low-oxygen condition also did not affect 3 beta-hydroxysteroid dehydrogenase/Delta 5-Delta 4 isomerase mRNA expression or the activity of the enzyme in the cells, regardless of the incubation period. The overall results indicate that a low-oxygen condition decreases P4 synthesis by attenuating P450scc production and P450scc activity in bovine luteal cells and suggest that oxygen deficiency is an essential condition for the progression of luteolysis in cattle.