INHIBITION OF VASOPRESSIN-SENSITIVE CAMP ACCUMULATION BY ALPHA-2-ADRENOCEPTOR AGONISTS IN COLLECTING TUBULES IS SPECIES DEPENDENT

The ability of alpha(2)-adrenoceptor agonists to inhibit vasopressin (VP)-stimulated cAMP accumulation in collecting tubules and to inhibit the antidiuretic effect of VP in rats is clearly established. However, in other species, such as the dog, alpha(2)-adrenoceptor-induced inhibition of VP action has not been convincingly demonstrated. In the present study, we examined the effects of epinephrine and other alpha(2)-adrenoceptor agonists on VP-stimulated cAMP accumulation in inner medullary collecting tubule cells and/or cortical collecting tubules from a number of species. Epinephrine, oxymetazoline, clonidine, and guanabenz inhibited VP-induced cAMP formation in rat inner medullary collecting tubule cells with IC50s ranging from 10 to 30 nM. However, epinephrine or guanabenz had no effect on VP-stimulated cAMP formation in cells from dog, pig, rhesus monkey, or human inner medulla. Similarly, epinephrine inhibited VP-induced cAMP accumulation in cortical collecting tubules dissected from rat kidneys but not from dog or rabbit kidneys. We conclude that there is a marked species difference in the ability of alpha(2)-adrenoceptor agonists to inhibit VP-induced cAMP formation at the tubular level. This may explain the difficulty in demonstrating an alpha(2)-adrenoceptor agonist-induced inhibition of VP action in other species such as dog and man.