THE INTERACTIVE EFFECTS OF VIP, PHI, GHRH AND SRIF ON THE RELEASE OF GROWTH-HORMONE FROM CULTURED ADENOHYPOPHYSEAL CELLS IN CATTLE

The effects of hypothalamic peptides [vasoactive intestinal peptide (V IP), peptide histidine isoleucine (PHI), growth hormone (GH)-releasing hormone (GHRH) and somatostatin (SRIF) on GH release from cultured bo vine adenohypophysial cells were studied. The cells were incubated for 2 h with the peptides after preincubation for 3.5 days. At doses from 10(-9) to 10(-7)M VIP, the amount of GH released was significantly gr eater than in the controls (P<0.05 to P<0.001). PHI (10(-10) to 10(-7) M) did not alter the bovine GH concentration in the media. Incubation with the media containing 10(-7) M GHRH, 10(-7) M VIP, and combined t reatment with the VIP plus GHRH increased GH by 186, 40 and 182%, resp ectively (P<0.001). Furthermore, although VIP-induced GH release was s ignificantly decreased by SRIF compared with the treatment with VIP al one (P<0.001), the VIP significantly blunted the inhibitory effect of the SRIF on GH release by 24% when compared with that of the SRIF plus GHRH without the VIP (P<0.05). GH release in combined treatments with VIP, GHRH and SRIF was significantly less than that of the VIP plus G HRH (P<0.001), but it was a significant 29% increase compared with the SRIF plus GHRH (P<0.05). The combined effects of the VIP (10(-7) M) w ith GHRH (10(-7), 10(-8) and 10(-10) M) significantly induced GH relea se compared with the controls (P<0.001), but no additive effect was no t observed when compared with the GHRH alone. The results indicate tha t VIP, but not PHI, acts directly on cultured adenohypophysial cells t o induce GH release in cattle.