Median Eminence Of Female Rats Research Articles

Serum MSH levels and the hypothalamic enzymes involved in the formation of MSH-RF during the estrous cycle in the rat.

Mitochondrial preparations from stalk median eminence of female rats were shown to contain an enzymatic system which yielded MSH-RF upon incubation with oxytocin. These enzymes were found present in the hypothalamus of rats at proestrus and estrus and absent in the other stages of the cycle. The MSH contained in plasma was also determined during the estrous cycle in the rat. Serum MSH was released on the morning of proestrus, reached a maximum value at 10.00 a.m., and remained high until 4.00 p.m. Thereafter serum MSH decreased to undetectable levels in the other stages of the cycle. MSH was released into the serum about tectable levels in the other stages of the cycle. MSH was released into the serum about 6 h before the proestrous peak of the gonadotrophin. A correlation was demonstrated between the hypothalamic enzymes responsible for the formation of both MSH-F-IF and MSH-RF and the MSH released into the serum.

Changes in plasma luteinizing hormone and prolactin after injection of vinblastine into the median eminence of the rat.

Colchicine, vinblastine and other tubulin-binding drugs (Borisy & Taylor, 1967; Bensch & Malawista, 1969) are known to block the release of insulin (Lacy, Howell, Young & Fink, 1968), posterior pituitary hormones (Douglas & Sorimachi, 1972), catecholamines (Poisner & Bernstein, 1971) and acetylcholine (Perisic & Cuenod, 1972). This implicates the cytoplasmic microtubule proteins (tubulins) in the mechanism of release of some cell secretory products. The present report presents evidence suggesting that vinblastine injected into the median eminence of female rats produces a prolonged inhibition of the output of luteinizing hormone (LH) releasing hormone and of prolactin inhibiting factor (PIF), thereby affecting gonadotrophin secretion. Holtzman female rats (200 g) showing at least two regular oestrous cycles, were anaesthetized with ether. The injections into the median eminence were performed stereotaxically through a Hamilton syringe with a 27-gauge needle. The experimental animals were injected with 3 μl (1 μl/min) of a 1 mM

Regulation of Formation and Proposed Structure of the Factor Inhibiting the Release of Melanocyte-Stimulating Hormone

Microsomal preparations from the stalk median eminence of female rats are shown to contain an enzymic activity that is responsible for the formation of MSH-release-inhibiting factor (MSH-R-IF). The amount of this activity remains constant throughout the estrous cycle. The corresponding mitochondrial preparations from the stalk median eminence contain another enzymic principle, estrous cycle-dependent, which competes with the enzyme present in the microsomal preparation for the same "substrate", and can thereby prevent the formation of MSH-R-IF. Several neurohypophyseal hormones, analogs, and peptide intermediates have been tested for their intrinsic MSH-R-IF activity and for their ability to be transformed into MSH-R-IF by incubation with microsomal preparations of stalk median eminence from male rats; it is concluded that the enzyme responsible for the formation of MSH-R-IF is an exopeptidase and that the release-inhibiting factor itself is a tripeptide. Oxytocin is converted by the incubation to (L)-prolyl-(L)-leucylglycinamide; nanogram amounts of this tripeptide inhibit the release of MSH from the pituitary both in vivo and in vitro.

Functional grafts of the anterior pituitary gland.

A study has been made of pituitary grafts placed into hypophysectomized adult rats under the median eminence of the tuber cinereum, under the temporal lobe of the brain and into the hypophysial capsule. Good union was obtained in all three sites, the grafts becoming richly vascularized and remaining viable for long periods. Grafts placed under the median eminence acquired vascular connexions with the primary plexus of the hypophysial portal vessels, whereas those under the temporal lobe of the brain and in the hypophysial capsule were not supplied by the portal system. Grafts placed under the temporal lobe of the brain and in the hypophysial capsule had greatly diminished, if any, function, but many of those placed under the median eminence of female rats had normal function as judged by ( a ) oestrous cycles, pregnancy, milk secretion (milk withdrawal from the nipple by the young was impossible, owing to neural lobe deficiency as shown by replacement therapy), ( b ) ovarian and adrenal weight and histology, ( c ) thyroid histology. Anterior pituitary tissue obtained from immature donors grafted into adult recipients showed hastened development. Similar tissue obtained from adult male donors grafted into adult female recipients was capable of maintaining normal oestrous cycles and pregnancy. A few experiments using male recipients indicated similar results concerning structure and function of the grafts. These results offer strong support to the view that the secretion of anterior pituitary hormones is under hypothalamic control, mediated by the hypophysial portal vessels.