Sexually diergic, dose-dependent hypothalamic-pituitary-adrenal axis responses to nicotine in a dynamic in vitro...

The hypothalamic-pituitary-adrenal cortical (HPA) axis modulates physiological responses to stress. We previously reported sexually diergic, dose-dependent HPA responses in vivo following nicotine administration: Male rats had greater arginine vasopressin (AVP) responses than females, and female rats had greater adrenocorticotropic hormone (ACTH) and corticosterone (CORT) responses than males. The goal of the present study was to further investigate sexually diergic, dose-dependent HPA responses following nicotine addition to an in vitro model of the HPA axis, so that hormone output could be determined at each level of the axis.

Hypothalami, pituitaries, and adrenal glands were harvested from male and female rats. One-half hypothalamus, one-half pituitary, and one adrenal gland were placed individually into three jacketed tissue baths connected by tubing and perfused in series with physiological medium. Sampling ports between tissue baths were used to collect buffer before and after addition of various doses of nicotine, for measurement of AVP and corticotropin-releasing hormone (CRH) from the hypothalamus bath, ACTH from the pituitary bath, and CORT from the adrenal bath. Hormones were measured by highly specific immunoassays.

Stable temperatures, flow rates, pH, and hormone baselines were achieved in the in vitro system. Consistent with our in vivo and earlier in vitro studies, nicotine added to the hypothalamus tissue bath significantly increased HPA responses in a sex- and dose-dependent manner: Males had greater AVP responses than did females, and females had greater CRH responses than did males. Sexually diergic ACTH and CORT responses were less apparent and were higher in females.

Our in vitro system accurately models in vivo HPA responses to nicotine in both sexes and thus represents a reliable method for investigating the effects of nicotine on components of the HPA axis. These studies may be pertinent to understanding the biological differences to nicotine between men and women smokers.