At the conclusion of the flight all rats were weighed and inspected. Anterior and posterior-intermediate lobes were collected, weighed, and individually frozen for assays. Plasma and pituitary growth hormone (GH), and prolactin were immunoassayed using GH and prolactin purified in-house as standards. Thyrotropin was assayed by a double antibody method, and luteinizing and follicle stimulating hormones by procedures employing NIAMDD (National Institute of
Arthritis, Metabolism and Digestive Diseases) rat standards. Adrenocorticotropic hormone (ACTH) was immunoassayed using the 3rd International Standard (porcine). Vasopressin was measured by a radioimmunoassay procedure and melanocyte stimulating hormone (MSH) by the bioassay method.

Results:

Although of modest extent, some perturbations of endocrine function were found in this investigation. The low plasma GH titers of flight animals either reflects the unusual sampling conditions at recovery or the effects of weightlessness. The larger adrenals of flight rats suggests they were secreting increased quantities of corticosterone over a significant part of the flight, which may have contributed to the smaller flight body weights by its protein catabolic effect. The adrenal hypertrophy of flight rats suggests these animals were secreting more ACTH and corticosterone during flight. There were no changes in either pituitary or plasma MSH suggesting that either the type or degree of stress was not adequate to stimulate MSH secretion.