Objectives:There are several cardiovascular, hormonal, and neural mechanisms regulating renin secretion that may be significantly affected by the physiological adaptations to the stresses of space flight and microgravity. The renin-angiotensin-aldosterone system defends the extracellular fluid compartment and blood pressure by promoting positive sodium balance and enhancing vasoconstrictor tone. Atriopeptin III augments shifts in extracellular fluid and may cause contraction of the extracellular fluid compartment by promoting diuresis and natriuresis. This study attempted to detect an alteration in renin secretion in space-flown rats.
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Approach:
Plasma samples were obtained after centrifugation of trunk blood collected at sacrifice of six flight and six ground control rats. A follow-up experiment with a group of sixteen rats was performed to test whether halothane anesthesia or the decapitation procedure affected renin release in either the flight or control rats. Plasma Renin Concentrations (PRC) were estimated by measuring the conversion of rat renin substrate to angiotensin I using radioimmunoassay.
Results:
No significant differences were found in PRC between flight and control animals, although, the flight mean was lower. Neither halothane anesthesia nor decapitation produced a significant increase in PRC above the levels measured in conscious control rats. Due to the twelve-hour delay between re-entry and sampling, all renin measured was probably secreted in the postflight period, so the PRC of flight rats do not indicate levels during flight, but only the levels obtained by flight animals during the twelve-hour recovery period. In summary, it was predicted that under conditions of microgravity, the tonic secretion of atriopeptin III may cause contraction of the extracellular fluid compartment by its diuretic and natriuretic actions. In addition, through its ability to inhibit renin secretion and interfere with the stimulation of aldosterone secretion, atriopeptin III may concomitantly depress the opposing influences of the renin-angiotensin-aldosterone that defend the extracellular fluid compartment.
Hartle DK, Inge WH. Plasma renin concentrations (PRC) of rats orbited for 7 days aboard NASA Spacelab 3. Abstract 83.30. 36th Annual Fall Meeting of the American Physiological Society; 1985 Oct 13-18; Buffalo(NY): 380.
Hartle DK, Inge WH. Plasma renin concentrations (PRC) of rats orbited for 7 days aboard NASA Spacelab 3. Abstract S-233-S-234. Proceedings of the Seventh Annual Meeting on the IUPS Commission on Gravitational Physiology; 1985 Oct 13-18; Niagara Falls(NY).
Hartle DK, Inge WH. Plasma Renin Concentrations (PRC) of rats orbited for 7 days aboard NASA Spacelab 3. Physiologist 1985; 28(6 Suppl):S233-4.
Content, Renin, plasma, trunk blood, rat, Renin substrate conversion to angiotensin I, radioimmunoassay.