The effect of transdermal corticosterone application on plasma corticosterone levels in pregnant Lacerta vivipara.

Relationships between hormones and behaviour can be explored by altering endogenous hormone levels, often through implantation of silastic tubing or osmotic pumps filled with a hormone or its agonists or antagonists. However, organisms in sensitive life-history stages (such as pregnancy) may be adversely affected by the surgical procedures associated with these manipulations, necessitating use of non-invasive techniques. We demonstrate that the application of a sesame oil-corticosterone mixture to the skin of pregnant female common lizards (Lacerta vivipara) elevates plasma levels of the hormone. Pregnant female L. vivipara were captured and treated daily for 1-20 days with the sesame oil-corticosterone mixture (experimental group) or with vehicle only (control group). Blood samples were collected and analyzed for corticosterone by radioimmunoassay. Baseline plasma corticosterone levels were elevated within 1 h in the experimental group. Similar levels ( approximately 145 ng/ml) were found over the subsequent 2 days, and by day 5 had risen significantly higher ( approximately 281.9 ng/ml), where they remained for the duration of the experiment. These increases are comparable to those found in other species using related techniques. No significant changes in plasma corticosterone levels occurred in the control group. Finally, corticosterone levels also were determined for untreated females that were captured, held overnight, sampled, and released to access to the natural range of basal corticosterone levels. Basal plasma levels of corticosterone in pregnant females varied among individuals independently of female body size or corpulence.