Summary
A radioimmunoassay (RIA) for testosterone (T) was found to be suitable for determination
in plasma of rats. Since the cross-reactive dihydrotestosterone levels were extremely
low both in males (130.8 ± 27.6 pmol/1) and females (189.4 ± 41.3 pmol/1), the procedure
measured T equally well, whether or not chromatography preceded the RIA. The method
met all requirements of precision, sensitivity, accuracy and specificity.
Basal levels of 5 male control groups (n ≈ 10) showed considerable variations from
a low of 6.86 ± 4.68 nmol/1 to a high of 16.26 ± 5.06 nmol/l. This high variability
may be the reason, at least in part, for the fact that moderate stress did not produce
always a significant decrease of T levels in males. However, after forced stress or
administration of adrenaline plasma T was significantly (p > 0.01) lower than in controls.
Gonadectomy lowered extremely plasma T levels both in males and females, whereas adrenalectomy
had no significant effect. These data demonstrate that the gonads are the main sources
of T in both sexes. The significant (p > 0.01) decrease of T levels after administration
of adrenaline, dexamethasone and ACTH in adrenalectomized males indicated that these
substances affect mainly the testicular synthesis of T.
In cyclic females, administration of ACTH produced no significant change in plasma
T levels. During pregnancy, there was a significant (p > 0.01) increase of plasma
T values from day 10 to day 18—19, followed by a decrease to day 22.
Key words
Rat - testosterone - stress - adrenaline - ACTH - dexamethasone
