Ala-Gly- and Val-Asp-[Arg8]-vasopressin: bovine storage forms of arginine vasopressin with natriuretic activity

Renal bradykinin and vasopressin receptors: ligand selectivity and classification

We studied the specific binding of radiolabeled bradykinin ([3H]BK) and vasopressin ([3H]AVP) to membrane preparations of bovine and porcine kidney medulla. [3H]BK reversibly labeled a single site (Kd = 1.06 nM) in bovine kidney medulla independently of [Mg2+]. The number of BK receptors in bovine kidney medulla, Bmax = 122 fmol/mg protein, is markedly (2- to 3-fold) higher than that reported in other tissues. Further characterization by ligand binding indicated that the bovine bradykinin receptor was the B2a subtype, pharmacologically related to B2a receptors expressed by human and rabbit tissues. In contrast, the specific binding of [3H]BK, but not [3H]AVP, to porcine kidney medulla (Kd = 0.32 nM, Bmax = 45 fmol/mg) was dependent upon the presence of enzyme inhibitors to prevent the rapid and selective degradation of bradykinin. Interspecies differences were revealed for renal medulla V2 vasopressin receptors with respect to their abundance and their affinity for several V2-selective ligands. In summary, (i) bovine kidney medulla is a convenient source of tissue for studying the B2a bradykinin receptor subtype; (ii) there are significant species-dependent differences in both the abundance of renal medulla B2a and V2 receptors and the ligand selectivity of V2 receptors; and (iii) these findings are significant in relation to the physiological and pathological roles of renal kinins and their interaction with the neurohypophysial peptide hormone system.

N-acetyl-vasopressin- and N-acetyl-oxytocin-like substances: isolation and characterization in the rat neurointermediate pituitary and presence in the brain

Abstract Post-translational modifications of vasopressin and oxytocin in pituitary and brain were investigated in view of recent evidence that oxytocin is partly N(alpha)-acetyfated in the bovine pineal gland. Two peptides were isolated from the neurointermediate lobe of the rat pituitary gland and characterized as N(alpha)-acetyl-vasopressin and N(alpha)-acetyl-oxytocin, based on chromatographic and immunological properties as well as the blocked N-terminus. In the neurointermediate pituitary the acetylated forms represented approximately 1% of the vasopressin and oxytocin contents. These two peptides were also detected in some, but not all, investigated brain areas. The highest degree of acetylation was found in the pineal gland. In all regions acetylation of oxytocin was more abundant than that of vasopressin. The data indicate that acetylation of vasopressin and oxytocin generally occurs as a post-translational modification. They support the concept that acetylation may represent a mechanism aimed to control bioactivity of the neurohypophyseal hormones.

Renal haemodynamic actions of pressor doses of lysine vasopressin in the rat

1. Dose-response effects of lysine vasopressin on renal haemodynamics were studied in conscious rats infused with 2.5% (w/v) dextrose solution at 5.8 ml/h. 2. Lysine vasopressin was maximally antidiuretic in the absence of a significant pressor effect at a dose of 2.5 pmol h-1 100 g body weight-1. Doses of vasopressin greater than this induced a dose-dependent increase in arterial blood pressure. 3. The clearance of p-aminohippurate (PAH) was not significantly changed by vasopressin, even at pressor doses. Rats pre-treated with indomethacin to inhibit prostaglandin synthesis showed a decrease in PAH clearance during the infusion of vasopressin at a dose of 30 pmol h-1 100 g body weight-1, and this suggests that the renal vasoconstrictor actions of vasopressin are attenuated by dilator prostaglandins. 4. Inulin clearance was unchanged by non-pressor doses of vasopressin but was decreased in a dose-dependent manner by pressor doses. A maximal effect was induced by a dose of 30 pmol h-1 100 g body weight-1 which decreased inulin clearance from 3.23 +/- 0.76 (mean +/- S.E. of mean) to 1.60 +/- 0.37 ml/min (P less than 0.02). A change in inulin clearance (from 3.42 +/- 0.46 to 2.17 +/- 0.33 ml/min, P less than 0.01) was also observed in rats pre-treated with indomethacin and infused with vasopressin at the same dose. The magnitude of the change was not significantly different from that observed in rats which were not treated with indomethacin. 5. Control rats infused with dextrose showed a slight but significant increase in sodium excretion during the course of the experiment. A similar natriuresis was observed in rats infused with non-pressor doses of vasopressin but was considerably enhanced in rats infused with pressor doses of the peptide. The antidiuresis induced by vasopressin remained maximal in rats infused with pressor doses. 6. Potassium and osmolal outputs were unchanged by non-pressor doses of vasopressin but significantly increased during administration of pressor doses. 7. It is concluded that pressor doses of lysine vasopressin do not alter total renal perfusion in conscious rats when the prostaglandin system is intact. Glomerular filtration is, however, decreased in a dose-dependent manner by these amounts but the mechanism is unclear.

Neurohypophysial peptides and the hippocampus. I. Vasopressin immunoreactivity in the rat hippocampus

Immunocytochemical studies have demonstrated that nerve fibres containing immunoreactive vasopressin project to many areas of the central nervous system. In the present investigation, the presence of immunoreactive arginine vasopressin (IR-AVP) in the hippocampus of Wistar rats was confirmed by radioimmunoassay. The vasopressin content of the dorsal hippocampus was 30.3 +/- 7.3 pg IR-AVP/mg soluble protein (mean +/- SEM, n = 9) and that of the ventral hippocampus was 81.4 +/- 8.3 pg IR-AVP/mg soluble protein (n = 9), while tissue from the cerebral cortex contained no detectable vasopressin. That the immunoreactivity was due to vasopressin was confirmed by its absence in hippocampal or cortical tissue from homozygous Brattleboro rats, which are genetically unable to synthesize vasopressin.

The effect of a vasopressin antagonist on the pressor response to histamine administered centrally

The mechanism for the pressor response to intracerebroventricularly (i.c.v.) administered histamine was studied. Histamine (HA), when injected intracerebroventricularly in rats, produced a dose-dependent increase in mean arterial pressure (MAP) which was subject to tachyphylaxis. Spinal transection at C-7 in the anesthetized rat did not attenuate the rise in blood pressure. The possibility that the release of 8-arginine vasopressin was responsible for the rise in blood pressure was explored. By pretreating conscious freely-moving rats with a specific antagonist to the vasopressor action of vasopressin viz., [1-beta-mercapto-beta, beta-cyclopentamethyleneproprionic acid), 2-(O-methyl) tyrosine] arginine-vasopressin, there was a statistically-significant attenuation of the pressor response to intracerebroventricularly administered histamine. The antagonist however, did not totally abolish the pressor response, regardless of the dose employed. Concomitant administration of hexamethonium and the vasopressin antagonist did not further attenuate the response. Previous adrenal demedullation did not diminish the response to intracerebroventricularly administered histamine, nor was there any evidence for release of angiotensin II since pretreatment with saralasin did not attenuate the cardiovascular response. These findings suggest that vasopressin along with other as yet undefined substances, are released from the central nervous system to produce the increase in blood pressure after intracerebroventricularly administered histamine.

Behavioral effects of intracerebroventricularly administered neurohypophyseal hormone analogs in mice

The neurohypophyseal hormones oxytocin and vasopressin evoke characteristic behavioral changes after intracerebroventricular injection in mice. These included the induction of excessive grooming and scratching in an unrestricted environment and of escape behavior in stressful situations. The structure-activity relations of 33 neurohypophyseal hormones and hormone analogs in the induction of these behavioral changes were examined. The results demonstrate that these effects generally parallel the vasoconstrictory effects of th peptides. It is suggested that the behavioral effects are mediated by a receptor that is closely related biochemically to the vasopressin receptors in blood vessels. They are not related to the long-term effects of neurohypophyseal hormones on learned behavior. A competitive antagonist of the short-term behavioral effects of these peptides is described. This analog also antagonizes some of the hormonal effects of vasopressin and related peptides.