AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 5 1250-R1256, Copyright © 1994 by American Physiological Society

ARTICLES

Circadian and estrous cycle-dependent variations in blood pressure and heart rate in female rats

H. Takezawa, H. Hayashi, H. Sano, H. Saito and S. Ebihara
First Department of Internal Medicine, Nagoya University School of Medicine, Japan.

To determine whether cardiovascular functions are controlled by the endogenous circadian system and whether they change with the estrous cycle in female rats, we measured mean arterial pressure (MAP), heart rate (HR), and spontaneous activity (ACT) of female rats using an implantable radiotelemetry device and a computerized data-collecting system. Under a 12:12-h light-dark (LD) cycle, these parameters exhibited daily rhythms that were entrained to the photic cycle. The patterns of the daily rhythms varied with estrous cycles, and variations were particularly marked in the proestrous stage. During the dark period of this stage, ACT levels were significantly higher, but HR was significantly lower than in other stages. Although the peak MAP occurred within 2 h after the onset of the dark phase in three of the estrous stages, it occurred around midnight in the proestrous stage. Such estrous cycle-dependent variations were eliminated by ovariectomy. The implantation of 17 beta-estradiol produced a gradual increase in MAP and an abrupt decrease in HR. During constant darkness, all three parameters were free running, maintaining the same internal phase relationships with each other as during LD cycles. These results indicate that daily variations in these parameters were controlled by the endogenous circadian oscillating system, that they vary with the estrous cycle in female rats, and that estrogen may be responsible for these estrous cycle-dependent variations.

This article has been cited by other articles:

				K. Morimoto, Y. Kurahashi, K. Shintani-Ishida, N. Kawamura, M. Miyashita, M. Uji, N. Tan, and K.-i. Yoshida Estrogen replacement suppresses stress-induced cardiovascular responses in ovariectomized rats Am J Physiol Heart Circ Physiol, November 1, 2004; 287(5): H1950 - H1956. [Abstract] [Full Text] [PDF]

				J. Pamidimukkala, J. A. Taylor, W. V. Welshons, D. B. Lubahn, and M. Hay Estrogen modulation of baroreflex function in conscious mice Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2003; 284(4): R983 - R989. [Abstract] [Full Text] [PDF]

				A. Alemayehu, L. Breen, and M. P. Printz A new inbred Wistar-Kyoto rat substrain exhibiting apparent salt sensitivity and borderline hypertension Am J Physiol Heart Circ Physiol, September 1, 2002; 283(3): H1181 - H1190. [Abstract] [Full Text] [PDF]

				B.-L. Zhang, E. Zannou, and F. Sannajust Effects of photoperiod reduction on rat circadian rhythms of BP, heart rate, and locomotor activity Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2000; 279(1): R169 - R178. [Abstract] [Full Text] [PDF]

				M. Makino, H. Hayashi, H. Takezawa, M. Hirai, H. Saito, and S. Ebihara Circadian Rhythms of Cardiovascular Functions Are Modulated by the Baroreflex and the Autonomic Nervous System in the Rat Circulation, September 2, 1997; 96(5): 1667 - 1674. [Abstract] [Full Text]