. Control of ovulation; proceedings of the conference held at Endicott House, Dedham, Massachusetts, 1960. Ovulation -- Regulation. Discussions 179 becomes anestrus after hysterectomy, and Dr. Hansel pointed out that even when ovulation is induced by administration of exogenous gonadotropins, the hysterectom- ized cow does not show behavioral estrus. This apparent species difference certainly invites further investigation. Our studies in the sheep therefore add this species to the list of animals in which a hypothalamic centre must be intact for heat to occur. This centre is probably stimulate
. Control of ovulation; proceedings of the conference held at Endicott House, Dedham, Massachusetts, 1960. Ovulation -- Regulation. Discussions 179 becomes anestrus after hysterectomy, and Dr. Hansel pointed out that even when ovulation is induced by administration of exogenous gonadotropins, the hysterectom- ized cow does not show behavioral estrus. This apparent species difference certainly invites further investigation. Our studies in the sheep therefore add this species to the list of animals in which a hypothalamic centre must be intact for heat to occur. This centre is probably stimulated directly by estrogens, and it is an inviting hypothesis that the aaion of progesterone in potentiating the heat-producing action of estrogen rests in some sort of a action on this brain centre. Certainly, there is ample precedent for an action of progesterone on the brain in the data presented by Dr. Sawyer this morning, and SITE OF HYPOTHALAMIC LESOHS W 9 EWES WITH NO HEAT PERIODS AND ACYCUC O^RIES. Fig. 3. progesterone therapy not only lowers the heat-producing threshold for estrogen, but is essential if heat periods are to recur c>'clically (Robinson, Endocrinology 55, 403, 1955). The brain also appears to be involved in the control of anterior pituitary secretion of gonadotropins in the ewe, as in other species. As indicated above, nine of the ewes in our series showed in addition to absence of beha\ ioral estrus, only small follicles and no corpora lutea in their ovaries. This fact indicates that periodic stimulation of the ovary was no longer present after the lesions were made. The sites of these lesions are shown in Fig. 3. These animals also had ventral hypothalamic lesions, but the common area of destruction in these sheep was more ventrally and caudally located than the common area in the sheep with the absent heat only. All these animals had some pituitary stalk damage, but the lesions probably did not produce their effect by damaging the pituitary bloo
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