Plasma antidiuretic hormone levels and kidney responsiveness to vasopressin in the jerboa, Jaculus orientalis.

The plasma antidiuretic hormone (ADH) concentration and the kidney medulla responsiveness to vasopressin were measured in adult jerboas ( Jaculus orientalis) in different states of hydration. In 15 jerboas adapted to 30 degrees and fed a dry diet, the average ADH concentration in blood plasma was 479 +/- 59 pg/ml, as measured by a radioimmunoassay. About 6 hr after receiving a 5% body wt water load by gavage, the plasma ADH concentration fell to 130 +/- 30 pg/ml in the 5 jerboas still producing hypertonic urine (1022 +/- 267 mosmol/liter) and to 41.5 +/- 8.4 pg/ml in the 6 jerboas producing hypoosmotic urine (157 +/- 6 mosmol/liter). In vitro biochemical experiments were performed on the kidney medullas from two groups of 5 jerboas fed a dry diet (group I) or a water-enriched diet (group II), respectively, for 4 to 7 weeks. Compared to group II, group I animals exhibited (a) higher plasma ADH values, 372 +/- 86 versus 76 +/- 25 pg/ml; (b) higher urine osmolarities (3817 +/- 638 versus 647 +/- 90 mosmol/liter); (c) some decrease in [3H]lysine-vasopressin (LVP) binding capacity to kidney membrane fractions (maximal binding: 0.4 versus 0.6 pmol [3H]LVP bound/mg protein); d) decreased adenylate cyclase responses to arginine-vasopressin, lysine-vasopressin, and oxytocin in kidney membrane fractions; and (e) weaker adenylate cyclase responses to arginine-vasopressin in microdissected pieces of the medullary thick ascending limb of Henle's loop. The values found for (a) the dissociation constant of [3H]lysine-vasopressin binding to membranes (KD); (b) adenylate cyclase sensitivity to the three neurohypophyseal hormones (KA); and (c) adenylate cyclase sensitivity to arginine-vasopressin (KA) in medullary collecting tubules and medullary thick ascending limbs are similar in the two groups of jerboas and roughly comparable to those previously reported for the rat kidney medulla. The reduced maximal adenylate cyclase responses to vasopressin in the jerboas fed a dry diet might indicate some physiological "down regulation" of the number of vasopressin-specific receptors in the kidney as a result of the huge ADH concentration present in blood plasma under these conditions. However, this desensitization is not sufficient to account for the production of hypoosmotic urine in spite of the relatively high ADH plasma levels which persisted after acute overhydration.