Effects of Intraarterial and Intrahypothalamic Injections of Pituitary Adenylate Cyclase- Activating Polypeptide on the Release of Growth Hormone in Goats

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The effects of intraarterial and intrahypothalamic injections of pituitary adenylate cyclase-activating polypeptide (PACAP) on the release of growth hormone (GH) were studied in female goats. The intraarterial injection of 0.5μg/kg body weight (BW) of PACAP failed to stimulate a significant GH release, whereas the dosages of 5 and 15μg/kg BW of PACAP significantly stimulated the GH release. The concentrations of GH 10min after the intraarterial injections of 5 and 15μg/kg BW of PACAP were significantly higher than the pre-PACAP GH concentrations (P<0.05). The intrahypothalamic injection of 0.5 and 5μg of PACAP significantly stimulated the GH release. The GH levels began to rise after the injections, and the concentrations of GH at 110 and 140min after the 0.5μg PACAP injection and 80, 110, 120 and 130min after the 5μg PACAP injection were significantly higher than the pre-PACAP concentrations (P<0.05). The area under the GH response curve for 2.5h after the intrahypothalamic injections of 5μg of PACAP was significantly greater than that of the control values (P<0.05). These results suggest that PACAP stimulates the GH release in goats by acting not only directly on the adenohypophysis but also indirectly through the hypothalamus.
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