Effects of hypothalamic extracts, neurotransmitters and synthetic hypothalamic releasing hormones on adenylyl cyclase activity in the lobes of the pituitary of the dogfish (Scyliorhinus canicula L.).

Neutralized acid extracts of the median eminence of the dogfish hypothalamus were found to cause a dose-related activation of adenylyl cyclase in all lobes of the dogfish pituitary. Equal concentrations of extracts of extrahypothalamic areas of the dogfish brain did not activate the enzyme. The putative neurotransmitters melatonin, serotonin, adrenaline, noradrenaline, dopamine and acetylcholine were without effect, as were the prostaglandins E1 and E2. The effects of synthetic mammalian hypothalamic hormones were also studied. Both thyrotrophin releasing hormone and gonadotrophin releasing hormone activated the ventral lobe enzyme, but had no effect on the adenylyl cyclase of the other three lobes. The tripeptide, Pro-Leu-Gly-NH2, a possible melanocyte-stimulating hormone release-inhibiting factor had no effect on the enzyme of the neurointermediate lobe. It is suggested that all four lobes of the dogfish pituitary may be under hypothalamic control and that this control is likely to be mediated by peptide hormones, as in mammals.