Biochemical characteristics of beta-adrenoceptors in rats after an 18-day spaceflight (LMS-STS78)

To ascertain whether there was autonomic adaptation with the development of adrenoceptor hypersensitivity under microgravity, the biochemical properties of the beta-adrenoceptors were determined using (125I)iodocyanopindolol (ICYP) binding in rats flown for 18 d onboard the space shuttle.

This study was performed on heart and kidneys of 3 groups of 12 animals: the flight and 2 ground control (vivarium and AEM) groups. To distinguish the possible role of the corticosteroids, half of each animal group was bilaterally adrenalectomized (ADX rats) with an aldosterone and corticosterone supplementation while the other half was SHAM operated.

The Scatchard analysis of the ICYP-binding in both organs revealed no significant alterations in the dissociation constant (Kd) and in the maximal binding capacity (Bmax) between SHAM flight and control groups. The Kd of the beta-adrenoceptors in the cardiac atria of the SHAM flight rats (74 +/- 5 pm) was significantly higher (p < 0.05) than in those of the ADX flight rats (60 +/- 3 pm) while the Bmax was nonsignificantly higher (1925 +/- 370 in SHAM flight rats vs. 1482 +/- 283 fmol x mg(-1) protein in ADX flight rats). No significant change was determined for the Bmax and Kd values in the kidneys of the ADX and SHAM flight rats.

This work performed on animals did not show any obvious effect of microgravity on the beta-adrenergic function in the heart and kidneys. Inflight rodent sacrifice protocols should definitely ensure assessment of the influence of microgravity on the animals.