Genetic approaches to the study of the regulation and actions of vasopressin

Vasopressin function in familial cranial diabetes insipidus

A family suffering from cranial diabetes insipidus, that extends over 4 generations, is described. Inheritance of polyuria was autosomal dominant. Vasopressin function was studied in members of the last 2 generations, 4 of whom had polyuria. Osmoregulation of vasopressin secretion was assessed by infusion of hypertonic saline. Plasma vasopressin remained undetectable in one patient, while 2 others had very blunted vasopressin responses to osmotic stimulation. Three non-osmotic stimuli were applied. Controlled hypotension produced by trimetaphan infusion and insulin-induced hypoglycaemia did not increase plasma vasopressin but apomorphine-induced nausea caused a minimal rise in plasma vasopressin to 0.7 pg/ml. Polyuria and thirst resolved with antidiuretic therapy in all patients studied. Congenital absence of vasopressin as in Brattleboro rats is unlikely to account for diabetes insipidus in this disorder since small increases in vasopressin have been demonstrated in these patients. In view of previous post-mortem findings, familial cranial diabetes insipidus is most likely to be due to degeneration of vasopressin-synthesizing neurones.

Cellular action of vasopressin in medullary tubules of mice with hereditary nephrogenic diabetes insipidus

Our previous studies (1974. J. Clin. Invest.54: 753-762.) suggested that impaired metabolism of cyclic AMP (cAMP) may be involved in the renal unresponsiveness to vasopressin (VP) in mice with hereditary nephrogenic diabetes insipidus (NDI). To localize such a defect to specific segments of the nephron, we studied the activities of VP-sensitive adenylate cyclase, cAMP phosphodiesterase (cAMP-PDIE), as well as accumulation of cAMP in medullary collecting tubules (MCT) and in medullary thick ascending limbs of Henle's loop (MAL) microdissected from control mice with normal concentrating ability and from mice with hereditary NDI. Adenylate cyclase activity stimulated by VP or by NaF was only slightly lower (-24%) in MCT from NDI mice, compared with controls. In MAL of NDI mice, basal, VP-sensitive, and NaF-sensitive adenylate cyclase was markedly (> -60%) lower compared with MAL of controls. The specific activity of cAMP-PDIE was markedly higher in MCT of NDI mice compared with controls, but was not different between MAL of control and NDI mice. Under present in vitro conditions, incubation of intact MCT from control mice with VP caused a striking increase in cAMP levels (>10), but VP failed to elicit a change in cAMP levels in MCT from NDI mice. When the cAMP-PDIE inhibitor 1-methyl-3-isobutyl xanthine (MIX) was added to the above incubation, VP caused a significant increase in cAMP levels in MCT from both NDI mice and control mice. Under all tested conditions, cAMP levels in MCT of NDI mice were lower than corresponding values in control MCT. Under the present experimental setting, VP and other stimulating factors (MIX, cholera toxin) did not change cAMP levels in MAL from either control mice or from NDI mice. The results of the present in vitro experiments suggest that the functional unresponsiveness of NDI mice to VP is perhaps mainly the result of the inability of collecting tubules to increase intracellular cAMP levels in response to VP. In turn, this inability to increase cAMP in response to VP is at least partly the result of abnormally high activity of cAMP-PDIE, a somewhat lower activity of VP-sensitive adenylate cyclase in MCT of NDI mice, and perhaps to a deficiency of some other as yet unidentified factors. The possible contribution of low VP-sensitive adenylate cyclase activity in MAL of NDI mice to the renal resistance to VP remains to be defined.

Ultrastructural observations on the hypothalamo-posthypophysical complex of the Brattleboro rat

The hypothalamo-posthypophysial complex of the homozygous Brattleboro rat is characterized by a hyperactivity of its neurons. The neurosecretory fibers, especially in the neurohypophysis, show numerous signs of autophagy and tubular proliferation of the axoplasmic reticulum. These structural alterations, as well as the nematosomes of nucleolus-like bodies encountered in the perikarya, may be related to the chronic hyperactivity of the neurons. They can be reduced by administration of exogenous vasopressin. The numerous liposomes in the pituicytes are paralleled in the neuronal perikarya by a great number of lysosomes. Small dense core vesicles observed in the neurosecretory endings and perikarya may indicate a secretory product distinct from oxytocin and vasopressin. In the homozygous Brattleboro rat, endings of the aminergic type are more numerous than in the normal rat. With respect to the role they may play in the secretory processes, their increase might be secondary to the vasopressin deficiency.