title: Effect of ovarian follicles on luteal regression in heifers.
abstract: Our objectives were to determine whether or not ovarian follicles contribute to spontaneous luteal regression in heifers and, if so, when during diestrus do follicles exert their effect. Thirty-one Holstein heifers having displayed at least one estrous cycle (19 to 21 d) were assigned, as available, to randomized blocks for a factorial experiment. Reproductive organs were exposed through a midventral incision on d 9, 12 or 15 postestrus (estrus = d 0). Visible follicles were electrocauterized and both ovaries were x-irradiated (1,500 rads) in treated heifers, whereas ovaries of controls were exteriorized but follicles were not destroyed and ovaries were not x-irradiated. In two additional heifers, the ovary containing the corpus luteum was exteriorized and x-irradiated on d 15 postestrus, but follicles were not electrocauterized. Jugular blood was collected before and every 8 h after surgery until d 24 postestrus. All heifers were ovariectomized on d 24 postestrus to inventory follicles and to weigh corpora lutea. No follicles (greater than or equal to 1 mm diameter) were observed in ovaries from treated animals and concentrations of estradiol-17 beta did not change over time, whereas different numbers of follicles were observed in ovaries from controls and concentrations of estradiol-17 beta increased (P less than .05) during proestrus. Hence, treatment destroyed follicles and prevented follicular development. On d 24 postestrus, corpora lutea from treated heifers (5.5 +/- .5 g) were heavier (P less than .001) than corpora lutea from controls (1.1 +/- .1 g), independent of day when follicles were destroyed.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003338:Corpus Luteum / Q000033:anatomy & histology / Q000528:radiation effects; D004958:Estradiol / Q000097:blood; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood; D003341:Luteolysis; D006080:Ovarian Follicle / Q000502:physiology*; D011247:Pregnancy; D011359:Proestrus; D011374:Progesterone / Q000097:blood; D014965:X-Rays
chemical_list: D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone