Search

These experiments were designed to demonstrate that pretreatment of newborn dogs with penicillin will enhance maturation of the renal organic anion transport system in vivo. Littermate pups were injected with procaine penicillin G (300,000 I.U./kg b.i.d. for 3 days) or saline before 2 weeks of age. Animals were surgically prepared on day 16 or 17. Transport of p-aminhippurate (PAH), as an indicator of renal organic anion transport, was quantified by the following procedures: 1) disappearance of a bolus injection from the plasma, 2) renal extraction and 3) rate of secretion in steady-state clearance experiments. The renal handling of insulin was measured simultaneously in all procedures for comparison. Penicillin-treated animals excreted a single intravenous bolus of PAH more rapidly than control animals, with the T1/2 decreased and the constant of elimination (Ke) increased. The extraction of PAH by kidneys of penicillin-treated animals was 165% that of controls. Similarly, the tubular secretion of PAH was increased in treated pups. These data confirm that in newborn animals the renal handling of organic anions in vivo is enhanced by pretreatment with a substrate of the secretory system.

By using standard clearance and stop flow techniques, studies were carried out in anesthetized dogs to clarify further the mechanism(s) of excretion of renin in urine. The clearance of renin was 0.61 +/- 0.19 ml/min in control experiments and increased significantly to 1.26 +/- 0.38 ml/min after furosemide. The fractional excretion of renin increased from 1.51 +/- 0.45% during control to 3.90 +/- 0.98% after furosemide. The rate of excretion of renin was increased 10-fold during furosemide diuresis associated with a 10-fold increase in plasma renin concentration. Extracellular fluid volume expansion also produced a diuresis but no increase in plasma renin or renin excretion. Hemorrhage produced a 3.5-fold increase in plasma renin concentration and a 200-fold increase in urinary excretion of renin. When renal artery perfusion pressure was reduced to one kidney, the excretion of renin in the urine from that kidney increased, whereas there was no significant change in the excretion from the contralateral kidney. Reduction in renal artery perfusion pressure was associated with a 3-fold increase in the concentration of renin in the renal vein from the experimental kidney but an insignificant 2-fold increase in the arterial plasma renin concentration. Stop-flow studies demonstrated that renin enters the urine with the glomerular filtrate. The decreased concentration of renin in samples from the proximal tubule suggests that renin is being metabolized and/or reabsorbed in this nephron segment. In the distal nephron, there appears to be a site in which renin may be added to the tubular fluid. The results of these studies suggest that renin excretion in the urine is a complicated process. Excretion of renin in the urine is related in part to plasma renin activity but probably more importantly to the rate of production of renin in the kidney.

The effects of anesthetic agents, nitrous oxide-oxygen, nitrous oxide-oxygen plus ketamine, pentobarbital sodium and halothane, were determined in piglets 6 to 76 hr of age. After observations of cardiovascular and renal function in the unanesthetized state, the drugs were administered and observations were repeated in the anesthetized state. All of the anesthetics caused a decrease in cardiac output and an increase in total peripheral resistance in the newborn piglet. Both nitrous oxide-oxygen plus ketamine and halothane produced a decrease in heart rate while pentobarbital caused an increase and halothane a decrease in systemic blood pressure. Changes in renal function were minimal. Changes in renal blood flow were inconsistent and renal vascular resistance was not modified by any of the drugs. There was little evidence of redistribution of intrarenal blood flow and no significant changes in glomerular filtration rate or sodium excretion. Plasma renin concentration increased after halothane. It was concluded that changes in renal and cardiovascular function due to anesthesia in the newborn were small. Differences between newborn and adult animals may be related to several factors including the state of development of the autonomic nervous system and species differences used in different studies.

The effects of furosemide, ethacrynic acid, hydrochlorothiazide and amiloride on renal function of newborn piglets, 5 to 10 days old, were evaluated. Furosemide and ethacrynic acid were the most effective diuretics. Furosemide infusion at 0.5 mg/kg/hr inhibited reabsorption of 21% filtered sodium and ethacrynic acid, 1 mg/kg/hr, increased fractional sodium excretion to 29%. Hydrochlorothiazide infusion produced a milder natriuresis than furosemide or ethacrynic acid. Infusion of hydrochlorothiazide at 1.0 mg/kg/hr increased fractional sodium excretion from 0.3% during the control period to 7.2%. Furosemide, ethacrynic acid and hydrochlorothiazide each increased potassium excretion to near 20 microEq/min. amiloride (1.0 mg/kg/hr) increased fractional sodium excretion from 0.2% during control period to 2.8% during drug infusion but did not affect potassium excretion. When infused in combination with furosemide and hydrochlorothiazide, amiloride increased the natriuresis and decreased the kaliuresis of both diuretics. It is concluded that the unanesthetized piglet is a good model for renal function of immature mammals and responds to diuretics in a manner qualitatively similar to adults.

The effects of furosemide on stimulation of renin secretion and urinary sodium excretion were studied in dogs pretreated with the prostaglandin synthetase inhibitors, indomethacin and meclofenamate. Pretreatment with these drugs failed to modify the natriuretic response to furosemide but completely blocked the rise in arterial plasma renin concentration produced by the diuretic. The organic acid probenecid did not affect either the natriuretic response or the increase in renin. In separate experiments, it was not possible to separate the effects of indomethacin on prostaglandin secretion, the renin-angiotensin system or renal hemodynamics. It is concluded that in the dog the natriuretic response to furosemide is not linked to the possible prostaglandin-induced increase in renal blood flow. Indomethacin apparently affects furosemide-induced renin secretion at both the vascular and macula densa sites. The data also suggest that the prostaglandins may be more important than the renin-angiotensin system in the modulation of intrarenal hemodynamics.