Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular resistance. Several lines of evidence suggest that CGRP plays a role in the vascular adaptations that occur during normal pregnancy; however, the effects of exogenous CGRP on systemic and regional hemodynamics during pregnancy remain unknown. Therefore, the purpose of this study was to determine the hemodynamic effects of systemically administered CGRP in adult pregnant (Day 19) and ovariectomized (ovx) rats using the radioactive microsphere technique. In addition, we also used ovariectomized rats treated for 3 days with estradiol (E₂), progesterone (P₄), E₂ P₄ in sesame oil, or oil only to assess if these hormones regulate the CGRP-induced hemodynamic changes. On the day of study, catheters were inserted into the left cardiac ventricle (through the right carotid artery), right jugular vein, and caudal tail artery. Hemodynamic studies using radioactive microspheres were then performed in conscious rats 3 h after recovery from anesthesia. Blood pressure and heart rate were continuously monitored, and left ventricular pressure was determined immediately prior to each microsphere injection. Microspheres labeled with either ¹⁴¹Ce or ⁸⁵Sr were injected prior to and 2 min following the i.v. bolus injection of CGRP (270 pmol/kg body weight [BW]). Mean arterial pressure (MAP) and total vascular resistance in pregnant rats was lower than in ovx rats, and this was further decreased with an i.v. bolus injection of 270 pmol CGRP/kg BW. Cardiac output was elevated with further increases upon CGRP administration in pregnant but not in ovx rats. The CGRP-induced changes in MAP, total vascular resistance, and cardiac output in E₂ P₄-treated rats were similar to that observed in Day 19 pregnant rats, indicating that CGRP effects on these parameters during pregnancy may be modulated by steroid hormones. Both pregnancy and E₂ P₄ treatment in ovx rats caused significant decreases in CGRP-induced resistance in mesenteric, coronary, and renal vasculature. Thus, the vasodilatory sensitivity to CGRP during pregnancy may be mediated through decreased total vascular resistance, particularly to coronary, mesenteric, and renal vascular beds. Thus, CGRP-induced vasodilatory effects may play a role in mediating vascular adaptations that occur during pregnancy and that steroid hormones may modulate these CGRP effects.