Effect of water and salt intake on pituitary catecholamines in the rat and domestic pig

The dopamine content of the combined neural and intermediate lobes of the rat pituitary gland was increased when the secretion of posterior lobe hormones was maximally stimulated by a restricted water intake followed by the administration of NaCl in the drinking water (dehydration). This was accompanied by vasodilatation in the posterior lobe and by an increase in the intensity of catecholamine fluorescence in the perivascular nerve fibres. The quantity of noradrenaline in the neural and intermediate lobes, which amounts to about 10% of that of dopamine, was also increased after dehydration. Bilateral removal of the sympathetic superior cervical ganglia did not prevent the rise in pituitary dopamine levels after dehydration but the perivascular catecholamine-containing nerve fibres were no longer detectable. The operation caused a decrease in the noradrenaline content of the neural and intermediate lobes by about 50% in rats on normal water intake and in dehydrated rats. Thus, one half of the noradrenaline present in the neural and intermediate lobes is not contained in vasomotor fibres or other nerve fibres with cell bodies in the superior cervical ganglion. The increase in pituitary dopamine levels after dehydration was also observed in domestic pigs. It is concluded that the increase in the concentration of dopamine in the combined neural and intermediate lobes that follows dehydration and salt-loading does not occur in the perivascular sympathetic nerve fibres and that it may be related to the fall in the pituitary content of oxytocin and vasopressin.