Elevation of intracellular cAMP by noradrenaline and vasoactive intestinal peptide in striated ducts isolated from the rabbit mandibular salivary gland.

Salivary gland intralobular ducts are responsible for the modification of the electrolyte composition of the primary fluid secreted by the acini. However, the intracellular messengers that regulate this and other intralobular duct cell processes have not been fully characterized. To investigate the possibility that cAMP-mobilizing agonists may be involved, intralobular (striated) ducts were isolated from the rabbit mandibular salivary gland by tissue dissociation and microdissection and maintained in tissue culture overnight. Individual duct fragments were stimulated with the secretory agonists noradrenaline, vasoactive intestinal peptide (VIP) and substance P and their cAMP content measured by acetylated radioimmunoassay. Both noradrenaline and VIP elevated intracellular cAMP content concentration dependently, but substance P did not. The response to noradrenaline was blocked by the beta-adrenoceptor antagonist propranolol, but not by the alpha-adrenoceptor antagonist prazosin. Application of the VIP analogue [D-p-Cl-Phe6, Leu17]-VIP decreased the VIP-induced cAMP response. These results demonstrate that striated intralobular duct cells possess beta-adrenoceptors and peptidergic receptors that are coupled to adenylate cyclase and activated by noradrenaline and VIP, respectively. By elevating ductal cAMP content, these agonists may regulate both the electrolyte content of the primary saliva and the secretion of protein(s) from the ducts.

Lack of effect of atrial natriuretic peptide and urodilatin on vasopressin-stimulated cyclic AMP production in microdissected rat inner medullary collecting ducts.

It is unclear whether the diuretic effects of atrial natriuretic peptide (ANP) result, in part, from an inhibition of the renal actions of vasopressin. Moreover, accruing evidence suggests that the kidneys themselves may produce an ANP-like peptide, urodilatin, which shares many of the renal actions of ANP. The mechanism underlying the diuretic action of urodilatin has not yet been examined. Accordingly, we have investigated the potential modulatory actions of both ANP and urodilatin on vasopressin-stimulated cyclic AMP (cAMP) production in microdissected inner medullary collecting duct (IMCD) segments of rat kidney. ANP and urodilatin alone (at 10(-8) or 10(-6) M) had no demonstrable effect on cAMP accumulation in IMCD segments. Moreover, neither ANP nor urodilatin (each at 10(-6) M) significantly altered either the profile or the absolute magnitude of the cAMP response stimulated by vasopressin. These findings indicate that neither ANP nor urodilatin interacts with the vasopressin-sensitive adenylate cyclase site in the rat IMCD to contribute to its diuretic actions.

Peptide hormone-stimulated second messenger production in the teleostean nephron.

Renal actions of arginine vasotocin (AVT) and atrial natriuretic peptide (ANP) in teleosts are poorly defined. Administration of these hormones changes renal function, largely explained by systemic vascular effects. The present experiments examine the potential direct action of these hormones on the teleost nephron. This has been assessed from the hormones' abilities to stimulate their second messenger systems within isolated nephroi of the rainbow trout Onchorhynchus mykiss. Following initial experiments to define the experimental conditions, AVT was found to induce a dose-dependent increase in cAMP content of a suspension of nephroi incubated for 10 min at 10 degrees; 10(-5) M AVT provoking an increase of 846% (SW) and 829% (FW) above basal cAMP accumulation of 88 and 125 pmol/mg protein, respectively. This V2-type receptor response to AVT (or AVP) has previously been considered to be present only in the tetrapod kidney. ANP evoked a dose-dependent stimulation of cGMP accumulation from 1.3 (SW) or 1.9 (FW) pmol/mg protein basal levels to 5806 and 4405% of these levels, respectively, at the highest concentration used of 3.3 x 10(-7) M. Further experiments using isolated glomeruli from the eel Anguilla anguilla localized at least a part of the response to ANP to a glomerular site.