RELATIONSHIP BETWEEN PENAL MASS AND ATRIAL-NATRIURETIC-PEPTIDE RELEASE .1. PARADOXICAL EFFECT OF UNILATERAL NEPHRECTOMY ON SERUM ATRIAL-NATRIURETIC-PEPTIDE IN RATS

Serial serum atrial natriuretic peptide (ANP) determinations were perf ormed in 15 uninephrectomized Charles River rats and in 15 sham-operat ed control animals during the 60 days following surgery. In a second g roup of 7 control and 7 uninephrectomized animals, housed in metabolis m cages, serum ANP, body weight, 24-hour urine volume, osmolality and sodium excretion were serially measured. In a third group of uninephre ctomized and control rats the effect of acute salt loading 24 h, 6 and 60 days after surgery on serum ANP was studied. No significant change s in ANP levels were observed during the 60 days following surgery in control animals. In the uninephrectomized animals a sharp drop in basa l ANP levels was evident 24 and 48 h after surgery, but increased leve ls of serum ANP were seen from day 6 to 28. Thereafter ANP returned to baseline levels for the rest of the study period. Urinary sodium excr etion decreased in the nephrectomized animals on days 1 and 2 followin g surgery. No such change was seen in the control animals during the s ame period. Body weight, 24-hour urine volume and urine osmolality wer e not statistically different in the nephrectomized vs. control rats a t any time and remained constant in each group throughout the experime ntal period. Central venous pressure (CVP) did not change significantl y in both groups 24 h and 6 days following surgery. CVP rose similarly in both groups immediately following saline loading and returned to p reload levels Ih later. Nephrectomized animals showed no change in ser um ANP Ih after saline loading performed 24 h after surgery, while in control animals acute saline load resulted, as expected, in a signific ant rise in serum ANP. 6 and 60 days following surgery, augmented ANP release Ih after acute salt loading was evident in both the nephrectom ized and control groups. We suggest that some as yet unknown mechanism exists through which the renal mass contributes to the control of ANP secretion by the cardiac atria.