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Abstract
Cardiovascular and sympatho-adrenomedullary responsiveness at rest and during stress
were studied in weight-matched, sexually mature male and female rats. At rest, although
there were no sex differences in cardiovascular parameters, females had two-fold higher
plasma levels of norepinephrine (NE) and epinephrine. Resting plasma levels of neuropeptide
Y-immunoreactivity (NPY-ir, a putative sympathetic cotransmitter and a vasoconstrictor)
were similar in both sexes. Stresses of handling and cold (4 degrees C) water exposure
induced greater pressor and tachycardic responses in males than in females. Males
but not females exhibited a protracted recovery from the stress-induced pressor responses
and a 2-fold increase in plasma NPY-ir suggesting that NPY release is sexually differentiated.
Only in males, low basal plasma NE and NPY-ir levels inversely correlated with greater
cold-induced pressor responses. Furthermore, in areflexic pithed rats, pressor adrenergic
and NPY responses were greater in males than in females suggesting the possibility
of "down"-regulation of vascular adrenergic receptors in females (due to elevated
circulating catecholamines) and "up"-regulation of NPY and adrenergic receptors in
males.