High hydrostatic and low oncotic interstitial pressures reduced proximal tubular fluid absorption and tubulo-glomerular feedback sensitivity, whereas low hydrostatic and high oncotic pressures increased them.
Do renal interstitial pressure conditions modulate proximal tubular fluid absorption and tubulo-glomerular feedback sensitivity in rats?
Renal interstitial pressure-volume conditions modulate renal function in response to extracellular fluid needs and blood pressure levels by altering proximal fluid absorption and tubulo-glomerular feedback sensitivity.
Rat micropuncture experiments have been performed to investigate the influence of renal interstitial pressure conditions on proximal tubular fluid absorption and on the tubulo-glomerular feedback mechanism. The feedback mechanism works by sensing the distal tubular fluid flow rate at the macula densa segment and adjusting the tonus of the arterioles with resulting changes in blood flow and glomerular filtration rate. It was found that in situations with high hydrostatic and low oncotic pressure within the interstitium like in saline volume expansion and post-nephrectomy situations, proximal tubular fluid absorption and the sensitivity of the tubulo-glomerular feedback control are reduced giving rise to increased urine production without activating the feedback mechanism. In situations with low hydrostatic and high oncotic interstitial pressures like in dehydration, hypotension and hypovolemia proximal fluid absorption and feedback sensitivity is increased, feedback sensitivity even so much that the mechanism is activated to reduce GFR even though the load to the distal portion of the nephron is reduced below normal. In this way renal interstitial pressure-volume conditions can modulate renal function in response to extracellular fluid needs and blood pressure level.
A. Erik G. Persson (1983) studied this question. Renal interstitial pressure conditions was evaluated on Proximal tubular fluid absorption and sensitivity of the tubulo-glomerular feedback control. High hydrostatic and low oncotic interstitial pressures reduced proximal tubular fluid absorption and tubulo-glomerular feedback sensitivity, whereas low hydrostatic and high oncotic pressures increased them.