No abstract

Two micrograms of f-endorphin (f3-lipotroPin61 il) injected intraventricularly in rats that had been treated with antiserum against somatostatin led to a 6-and 10-fold stimulation of the concentration of plasma growth hormone (somatotropin) measured 10 and 20 min after injection of the peptide, whereas-400 ug of methionine-enkephalin led to a 4-to 6-fold increase of levels of plasma growth hormone at 10 min with a rapid return to basal levels at later time intervals. At doses of 5 and 25 pg, A-endorphin led to a 20-to 30-fold stimulation-of levels of plasma growth hormone, the maximal effect being measured between 20 and 30 min after injection. These data su 'est the possible role of the endogenous opiate-like peptides in the control of growth hormone'secretion. Morphine is well known to be a potent stimulus of growth hormone (GH; somatotropin) release in the rat (1-3). This effect of the opiate is likely to be mediated by increased release of GH-releasing activity from the hypothalamus (4).Following reports of the presence of endogenous opiate activity in the brain (5-7), the pentapeptide H-Tyr-Gly-GlyPhe-Met-OH (Met-enkephalin) has been isolated from porcine brain (8). This peptide has'been shown to have potent opiate activity (8) and to bind to the opiate receptor (9, 10).The

No abstract

The plasma PRL and TSH responses to TRH injected iv at different stages of the estrous cycle in normal rats under Surital anesthesia were maximal during the afternoon of proestrus and morning of estrus and lowest on diestrus I. As calculated from the areas under the plasma response curves, a 10-fold difference was found between the maximal and minimal PRL responses while a 2-fold difference was measured for TSH. The plasma PRL and TSH responses to TRH showed a correlation with the binding of [3H]TRH to anterior pituitary gland, a 3-fold difference being observed between the minimal binding measured on the morning of diestrus II and the maximal value found on the evening of proestrus. Contrary to findings with LHRH and LH, repeated injections of a small dose (10 ng) of TRH in the afternoon of proestrus abolished PRL and TSH responses to subsequent injection of the neurohormone.