Effects of neural peptides on the release of pituitary hormones and their fluctuations within the brain in domestic animals.

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1. The hypothalamus and pituitary tissues of cows were collected from a local slaughter house and superfused them in order to investigate the effects of neural peptides on the release of pituitary growth hormone (GH), luteinizing hormone (LH) and prolactin (PRL). Mature female goats, a ruminant animal, were also used similarly in a superfusion study. The neural peptides used for the experiments were vasoactive intestinal peptide (VIP), Substance p (SP), growth hormone releasing factor (GRF), cholecystokinin (CCK), peptide histidine isoleusine (PHI), angiotensin II (A II). In addition to these peptides, a posterior pituitary tissue extract was used for the superfusion study. GH, LH and PRL contained in the perifusion efflux were measured by radioimmunoassays. (1) VIP released GH in a dose dependent manner acting directly to the pituitary when dilution rates from 10^<-6>M to 10^<-8>M VIP were used for the perifusion. This rise in GH level declined soon after cessation of VIP perifusion. … More GRF released GH from the pituitary in a dose dependent manner from 10^<-6>M to 10@>D1-11@>D1M GRF. GRF released GH continuously even after the cessation of GRF perifusion for at least 80 min when dilution rates from 10^<-6>M to 10^<-8>M VIP were used for perifusion (2) In the similar perifusion system goat pituitary tissues released GH in a dose dependent manner in response to perifusion of 10^<-6>M to 10^<-9>M VIP. (3) 10^<-8>M CCK inhibited release of LH from perifused pituitary tissues from castrated oxen, while 10^<-6>M CCK stimulated release of LH. (4) Possible candidates for prolactin releasing factor(PRF), VIP, SP, CCK, PHI and A II failed to release PRL from the perifused pituitaries of cows at a dose level of 10^<-7>M, but 10^<-7>M SP inhibited PRL release. Posterior pituitary extracts from cows released pituitary PRL remarkably when 1/2 to 1/8 equivalent posterior pituitary extracts were perifused on the hypothalamus-pituitary tissues. It is suggested that PRF could be contained in the posterior pituitary in cows. Using a push-pull canula technique, a pulsatile release of LHRH was found in the pig hypothalamus and the goat hypothalamus. Less