Bombesin produces hypothermia in hypophysectomized rats

Intracerebroventricular administration of bombesin, a naturally-occurring peptide, produces hypothermia in the rat. To determine whether a pituitary-dependent step is necessary for this effect, the thermoregulatory response was followed in hypophysectomized and intact rats maintained at room temperature. Significant hypothermia was produced in both experimental groups. This study supports an extra-pituitary mechanism for bombesin-induced hypothermia.     

The hypothalamo-hypophysial system of hypophysectomized rats

Summary The median eminence (ME) of hypophysectomized rats was studied by means of light and electron microscopy. Paraldehyde-fuchsin (PAF)-positive material is seen in the external zone (EZ) of the ME 2–5 days after the operation. Its amount gradually increases especially in the caudal part of the ME during the following few days. Some PAF-positive fibers make contact with the subependymally located blood capillaries. In the most caudal region of the recessus infundibuli they penetrate into the third ventricle. PAF-positive material decreases markedly from the ME of rats two months after hypophysectomy and exposure to a 1% salt load. Fibers of types A₁, A₂ and B containing granules of 120–220 nm, 100–150 nm and 80–100 nm in diameter, respectively, are seen in the EZ of the ME in hypophysectomized rats, although almost exclusively A₂- and B-type structures make contact with the primary portal capillaries in intact animals. All types of neurosecretory fibers establish contact with the subependymal nonfenestrated blood capillaries and penetrate the recessus infundibuli. Some neurosecretory terminals of different types make direct contact with the glandular cells of the pars tuberalis or are separated from them by a thin basal lamina. It is assumed that mainly neurosecretory fibers of types A₂ and B are permanently connected with the primary portal capillaries in the EZ of the ME in intact mammals, while the overwhelming majority of fibers of A₁-type shows ingrowth during the course of postoperative reparation. The possible physiological significance of the described changes is discussed.     

Maternal aggression exhibited by hypophysectomized parturient mice

Surgical removal of the pituitary gland (hypophysectomy) in parturient mice virtually eliminated suckling-induced prolactin (PRL) release but failed to alter the initiation of maternal aggression toward adult male intruders. Thus, contrary to common speculation, the release of suckling-induced pituitary hormones, especially PRL, is not essential for the onset of fighting behavior in postpartum mice.     

Immunohistochemical analysis of EGF in epiphyseal growth plate from normal,hypophysectomized, and growth hormone-treated hypophysectomized rats

Epiphyseal growth plate cartilages from the proximal tibia of normal, hypophysectomized, and growth hormone (GH)-treated hypophysectomized rats were subjected to immunohistochemistry for detection of epidermal growth factor (EGF). In the normal growth plate, EGF was distributed mainly in the proliferative zone. Hypophysectomy resulted in considerable atrophy of the chondrocytes and the cartilage matrix (a decreased number of mature-type chondrocytes and a decreased ratio of proliferating to hypertrophic chondrocytes) and a significant diminution of EGF immunoreactivity. Treatment with GH reversed these effects of hypophysectomy, causing an increased thickness of the growth plate and EGF-reactive sites in all chondrocyte layers. The most intense immunostaining for EGF, however, was frequently seen in the nuclei of chondrocytes with flattened appearance. It appears that EGF could be incorporated or synthesized in chondrocytes having marked mitogenic activity. The present results, taken with previous data on EGF involvement in growth of cartilaginous tissue in vivo and in vitro, strongly suggest that EGF-immunoreactive chondrocytes are involved in cartilage proliferation and growth under the specific influence of GH.     

Effects on extrahepatic UDP-glucuronosyltransferases in hypophysectomized rat

The effects of hypophysectomy on hepatic and extrahepatic UDP-glucuronosyltransferase activities in adult male rats were observed. UDP-glucuronosyltransferase activities toward 1-naphthol decreased to 20-30% of control in the liver, kidney, lung, and testis. The mRNA of UGT1A6, which is an isoform contributing to the glucuronidation of various phenolic xenobiotics such as 1-naphthol, were decreased drastically in the liver, kidney, and testis by hypophysectomy. However, while bilirubin UDP-glucuronosyltransferase activity in the liver intensified, there was only a slight increase in the activity in the kidney and no alteration in the lung. The mRNA of UGT1A1, which is an isoform contributing to the glucuronidation of bilirubin, increased significantly in the liver and slightly in the kidney after hypophysectomy. These inductions and reductions in enzymatic activities and mRNA levels in each tissue were restored to control levels by intermittent injections of rat growth hormone. Interestingly, while hepatic UGT activity toward bisphenol A remained constant in hypophysectomized rats, the testicular UGT activity declined to 10-15% of control but returned to normal levels following growth hormone treatment, suggesting that an unknown UGT isoform (s) mediates bisphenol A glucuronidation in the testis. These results indicate that the expression of extrahepatic UGT is isoform-specific and regulated differentially in tissues by the pituitary gland.     

The maintenance of pregnancy in hypophysectomized goats

Pregnancy in goats is maintained after hypophysectomy at about Day 90 of gestation by injection of 20 mg progesterone or 1 mg LH/day, but not by 5 mg prolactin/day.