Removal and excretion of immunoreactive rat growth hormone by the isolated kidney

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Abstract
The renal uptake of immunoreactive rat growth hormone (rGH), molecular weight 21,500 daltons, was examined in the isolated perfused rat kidney to determine whether peritubular removal of a protein greater than 12,000 daltons occurs and to assess the functional characteristics of renal GH uptake. Organ clearance of rGH (OCGH) in control kidneys was 1,039 +/- 99 microliters/min and was unaffected by an excess of insulin but markedly depressed by col (10 degrees C( and KCN. Although glomerular filtration rate (GFR) did not differ significantly from OCGH in the control rats, we suspected that filtration could not account for all the rGH removed because of glomerular protein sieving. However, GFR was significantly less than OCGH with cold and KCN treatment, indicating the occurrence of peritubular removal. In nonfiltering kidneys, rGH removal exceeded that of [14C]inulin (P less than 0.05), demonstrating peritubular rGH removal. Tubular absorption of rGH was unaffected by insulin but markedly depressed by cold and KCN. We conclude that rGH is removed from the renal circulation mainly by the glomerular filtration-tubular absorptive pathway, but, in addition, as with smaller proteins, that peritubular removal occurs.