Vasopressin and 1-deamino-8-D-arginine-vasopressin (DDAVP) reduce elevated plasma catecholamine levels in rats with hypothalamic deafferentation.

1. Anterolateral cut (ALC) of the medial basal hypothalamus (MBH) in rats produces an elevation of plasma catecholamine levels, especially of norepinephrine (NE), in unstressed animals and a more pronounced rise of plasma NE levels in response to immobilization (IMO). Animals with ALC have a destroyed corresponding vasopressin (AVP) and other peptides containing innervation of the median eminence and the posterior pituitary, resulting in the prevention of increased AVP secretion during the early intervals of IMO. 2. The administration of AVP (Pitressin, 7 days, 1 IU per rat i.m.) or of 1-deamino-8-D-arginine-vasopressin (DDAVP), an AVP analogue without pressoric activity, taken in drinking water (about 100 micrograms per day) was almost equally potent in decreasing the elevated water consumption and plasma NE levels in unstressed rats with ALC. However, the stress-induced potentiation of plasma NE levels in rats with ALC was not influenced by AVP substitution and only partly reduced by DDAVP in the late IMO intervals. 3. The lack of circulating vasopressin is the main factor in the mechanism of increased activity of the sympathoadrenal system induced by ALC in unstressed rats. 4. The regulation of sympathoadrenal activity by vasopressin and DDAVP in rats with ALC seems to be mediated predominantly by V2-subtype receptors. 5. In stressed rats with ALC the potentiation of plasma NE levels was not reduced after AVP or DDAVP administration, suggesting that some addition regulatory mechanisms were involved.

Effect of metoclopramide therapy on arginine vasopressin excretion and renal water handling in premature infants.

The role of endogenous dopamine (DA) in regulating arginine vasopressin (AVP) release and renal water excretion was studied in 10 premature infants with a mean birth weight of 1,341 g (range 1,150-1,660 g) and a mean gestational age of 30.2 weeks (28-33 weeks), who were given metoclopramide (MTC), a specific DA antagonist. It was demonstrated that in response to MTC urine flow rate increased significantly from a basal value of 0.90 +/- 0.07 to 1.27 +/- 0.09 ml/min/1.73 m2 (mean +/- SE; p less than 0.01), urinary sodium excretion from 6.10 +/- 1.47 to 11.7 +/- 2.24 microEq/min/1.73 m2 (p less than 0.025) and osmolar clearance from 0.38 +/- 0.044 to 0.600 +/- 0.075 ml/min/1.73 m2 (p less than 0.01). MTC administration did not cause any alterations in free water clearance, whereas urinary AVP excretion fell significantly from 49.38 +/- 10.13 to 32.66 +/- 6.53 ng/min/1.73 m2 (p less than 0.05) after MTC. It is concluded that, contrary to adults, in low birth weight premature infants endogenous DA is enhancing rather than inhibiting AVP release and the MTC-induced water diuresis is independent of the fall of AVP since free water clearance remained unaltered after MTC.

Water deprivation for 24 hours increases selectively blood flow in posterior pituitary of conscious rats.

Blood flow was measured by means of 125I-Antipyrin distribution and was found to be increased in the posterior pituitary of conscious rats following water deprivation for 24 h as compared to either normohydrated control or to force hydrated rats (2.86 ml min-1 g-1 vs. 2.36 ml or 2.08 ml, respectively). Other parameters of systemic haemodynamics, blood flow in the brain or in the hypothalamus and in anterior pituitary did not differ in three experimental groups of rats subjected to various water intake. The increased blood flow in the posterior pituitary in dehydrated rats presumably parallels the locally intensified metabolic rats due to the enchanged stimulation of the antidiuretic hormone release.