Effect of Antidiuretic Hormone and Dibutyryl cAMP upon the Urinary Concentrating Capacity in Neonatal Piglets

Abstract

Summary: In 18-one-day-old anesthetized piglets, the effects of 1-deamino-8-D-arginine-vasopressin (DDAVP) with and without administration of dibutyryl adenosine 3′:5′-monophosphate (DBcAMP) upon the urinary concentrating system were studied. Supramaximal doses of 20 μg DDAVP per kg body weight did not affect fractional water and fractional urea excretion, urinary flow rate, and relative urinary osmolarity. The same dose combined with DBcAMP (0.2 mg/kg body weight per min) changed these parameters significantly. This increase in the responsiveness of the urinary concentrating system to DDAVP by DBcAMP was paralleled by a significant increase in urinary and plasma cyclic adenosine 3′:5′-monophosphate concentration and a tremendous increase in the medullary cyclic adenosine 3′:5′-monophosphate content (2.5 × 10⁵ pmoles/g medulla) as compared to the controls (6.4 × 10² pmoles/g medulla) and the animals which received DDAVP without DBcAMP (8.0 × 10² pmoles/g medulla). To exclude the possibility that the increased medullary cyclic adenosine 3′:5′-monophosphate production might be caused by degradation of the dibutyryl derivative, in vitro studies with [³H]DBcAMP were performed. Incubation of labeled DBcAMP with a renal medulla homogenate of a 1-day-old piglet for 30, 60, and 90 min did not decrease the amount of [³H]DBcAMP.

Speculation: The reduced accumulation of cyclic adenosine 3′:5′-monophos-phate in response to antidiuretic hormone within the renal collecting duct cells seems to be an important reason for the reduced concentrating capacity of the neonatal kidney.

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