Adrenal function in the Mongolian gerbil (Meriones unguiculatus): influence of confinement stress upon glucocorticosteroid, progesterone, dehydroepiandrosterone, testosterone and androstenedione plasma levels, adrenal content and in-vitro secretion

Abstract

The pattern of adrenal steroid secretion and the response to confinement stress were investigated in male Mongolian gerbils (Meriones unguiculatus). Steroid levels of glucocorticosteroids (GC), progesterone (P), dehydroepiandrosterone (DHEA), testosterone (T) and androstenedione (A) in plasma, adrenal tissue and superfusates of adrenals superfused in-vitro were measured by radioimmunoassay. The sensitivity of the assay systems and the low cross-reactivity of the antisera used allowed the determination of steroid levels in small samples (5-200 microliters), without prior chromatography. GC plasma levels were much higher than values of P, DHEA, T or A (176.7, 2.4, 3.3, 2.6 and 2.8 ng/ml, respectively). Confinement stress resulted in a significant increase of GC and DHEA plasma levels; similarly, adrenal content of GC, DHEA and P was markedly increased. In contrast, the applied stress factor had no significant effects on either plasma levels of P, T or A or on adrenal T or A content. Compared to plasma levels or adrenal content, amounts of steroids secreted from adrenals superfused in-vitro were very low (GC: 57.1, P: 2.1, DHEA: 23.0, T: 1.8, A: 3.0 pg/mg/min, respectively). Confinement stress significantly stimulated GC, P and DHEA secretion in-vitro but had no effects on T or A release. The secretion of GC, P, DHEA and T, but not of A was significantly increased by in-vitro stimulation with 0.01-10.0 mIU (1-24) ACTH. Interestingly, the amounts of GC and P, and of GC and DHEA secreted from incubated adrenal slices stimulated with (1-24) ACTH and from adrenals of controls and stressed gerbils superfused in-vitro were significantly correlated. By measuring steroid plasma levels and profiles of steroids secreted from adrenocortical and testicular tissue it now seems possible to characterize in more detail the effects of chronic intermittent stress upon the adrenalgonadal axis and the possible interrelationship between glucocorticosteroid and androgen secretion, especially in small laboratory animals from which only limited amounts of blood can be obtained repeatedly.