Timing within the menstrual cycle, sex, and the use of oral contraceptives determine adrenergic suppression of NK cell activity

Physiological responses that involve adrenergic mechanisms, such as stress-induced changes in cardiovascular indices, were reported to fluctuate along the menstrual cycle. Metastatic development following surgery was also reported to vary according to the menstrual phase during which a primary breast tumour was removed. Natural killer (NK) cells are believed to play an important role in controlling metastases. Our recent studies in rats demonstrated that adrenergic suppression of NK activity and of resistance to metastasis is more profound during oestrous phases characterized by high levels of oestradiol. In the current study in humans, we examined the in vitro impact of a β-adrenergic agonist, metaproterenol (MP), on NK activity, comparing blood drawn from (a) women tested at 3-4 different phases of their menstrual cycle (n = 10), (b) women using oral contraceptives (OC) (n = 10), and (c) men (n = 7). NK activity in each blood sample was assessed in the presence of 5 different concentrations of MP (10^-8 M to 10^-6 M), and in its absence (baseline). The results indicated marked group differences in the magnitude of NK suppression by MP: EC₅₀ was 2.6-fold lower in the luteal phase compared to the follicular phase, and 1.8-fold lower in OC users compared to men, who were least susceptible to the effects of MP. No significant group differences or menstrual effects in baseline levels of NK activity were evident. These findings provide the first empirical evidence for menstrual regulation of adrenergic impact on cellular immune competence. Relevance of these findings to the relation between the timing of breast cancer excision within the menstrual cycle and survival rates is discussed. (C) 2000 Cancer Research Campaign.