Endocrinology, Vol 136, 512-520, Copyright © 1995 by Endocrine Society

ARTICLES

The hypothalamic-pituitary-adrenal axis in rat pregnancy and lactation: circadian variation and interrelationship of plasma adrenocorticotropin and corticosterone

HC Atkinson and BJ Waddell
Department of Anatomy and Human Biology, University of Western Australia, Nedlands, Perth.

The circadian variation in immunoreactive (I-) ACTH and corticosterone was studied at several stages throughout rat pregnancy and compared with those before pregnancy and during lactation. Serial blood samples were obtained from chronically cannulated, conscious rats at 2- to 3-h intervals beginning at 0800 h at diestrus of the cycle; on days 2, 6, 10, 14, 18, and 22 of pregnancy (term = day 23); and on day 4 of lactation. Plasma I-ACTH and corticosterone were determined in all samples, and indices of their circadian variation (acrophase, mesor, and amplitude) were derived by cosinor analyses within each rat. A circadian variation in corticosterone was clearly evident in all groups, with individual cosinor r2 values being consistently high. Plasma I-ACTH also exhibited distinct circadian variation up to day 14 of pregnancy, but the cosinor r2 value then fell (P < 0.05, by analysis of variance) and remained low during lactation. Mesor levels (midpoint of the derived circadian range) of I-ACTH fell (P < 0.05) by 34% to 20.6 +/- 2.4 pg/ml by day 2 of pregnancy; corticosterone also fell (P < 0.05) by 34% to 141 +/- 27 ng/ml, and both changes were due primarily to reductions in peak levels. I-ACTH mesors then remained effectively unchanged for the remainder of pregnancy, but mesor corticosterone increased progressively after day 10 to reach a maximum of 286 +/- 28 ng/ml by day 22, and this rise was due to elevations in both trough and peak corticosterone levels. Further changes occurred after parturition, with mesor I-ACTH increasing more than 2-fold between day 22 of pregnancy and day 4 of lactation, whereas mesor corticosterone declined by more than half over the same period. Plasma corticosterone and I- ACTH were positively associated within rats in all groups (P < 0.01), but the common slope of this association increased considerably after midgestation, indicative of higher corticosterone levels for a given concentration of I-ACTH. In summary, this study identifies marked changes in the hypothalamic-pituitary-adrenal axis during rat pregnancy and lactation. Although a circadian variation in corticosterone was observed throughout, that in plasma I-ACTH was evident early in pregnancy but declined after midgestation. Absolute concentrations of plasma I-ACTH and corticosterone fell in parallel early in pregnancy, but corticosterone subsequently increased without any change in I- ACTH.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				H. Ashdown, S. Poole, P. Boksa, and G. N. Luheshi Interleukin-1 receptor antagonist as a modulator of gender differences in the febrile response to lipopolysaccharide in rats Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2007; 292(4): R1667 - R1674. [Abstract] [Full Text] [PDF]

				A. J. Tilbrook, A. I. Turner, M. D. Ibbott, and I. J. Clarke Activation of the Hypothalamo-Pituitary-Adrenal Axis by Isolation and Restraint Stress during Lactation in Ewes: Effect of the Presence of the Lamb and Suckling Endocrinology, July 1, 2006; 147(7): 3501 - 3509. [Abstract] [Full Text] [PDF]

				S. L. Moore and J. E. Fewell Mifepristone (RU38486) influences the core temperature response of term pregnant rats to intraperitoneal lipopolysaccharide Exp Physiol, July 1, 2006; 91(4): 741 - 746. [Abstract] [Full Text] [PDF]

				A. Mouihate, S. Ellis, E.-M. Harre, and Q. J. Pittman Fever suppression in near-term pregnant rats is dissociated from LPS-activated signaling pathways Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2005; 289(5): R1265 - R1272. [Abstract] [Full Text] [PDF]

				S. Ma, M. J. Shipston, D. Morilak, and J. A. Russell Reduced Hypothalamic Vasopressin Secretion Underlies Attenuated Adrenocorticotropin Stress Responses in Pregnant Rats Endocrinology, March 1, 2005; 146(3): 1626 - 1637. [Abstract] [Full Text] [PDF]

				A. J. Douglas, P. J. Brunton, O. J. Bosch, J. A. Russell, and I. D. Neumann Neuroendocrine Responses to Stress in Mice: Hyporesponsiveness in Pregnancy and Parturition Endocrinology, December 1, 2003; 144(12): 5268 - 5276. [Abstract] [Full Text] [PDF]

				M. N. Berg, A. M. Dharmarajan, and B. J. Waddell Glucocorticoids and Progesterone Prevent Apoptosis in the Lactating Rat Mammary Gland Endocrinology, January 1, 2002; 143(1): 222 - 227. [Abstract] [Full Text] [PDF]

				A. Wigger, P. Lörscher, I. Oehler, M. E. Keck, T. Naruo, and I. D. Neumann Nonresponsiveness of the Rat Hypothalamo-Pituitary-Adrenocortical Axis to Parturition-Related Events: Inhibitory Action of Endogenous Opioids Endocrinology, June 1, 1999; 140(6): 2843 - 2849. [Abstract] [Full Text]

				P. J. Burton and B. J. Waddell Dual Function of 11ß-Hydroxysteroid Dehydrogenase in Placenta: Modulating Placental Glucocorticoid Passage and Local Steroid Action Biol Reprod, February 1, 1999; 60(2): 234 - 240. [Abstract] [Full Text] [PDF]

				C. M. Telleria, J. Ou, N. Sugino, S. Ferguson, and G. Gibori The Expression of Interleukin-6 in the Pregnant Rat Corpus Luteum and Its Regulation by Progesterone and Glucocorticoid Endocrinology, August 1, 1998; 139(8): 3597 - 3605. [Abstract] [Full Text] [PDF]

				R. J. Windle, S. A. Wood, N. Shanks, S. L. Lightman, and C. D. Ingram Ultradian Rhythm of Basal Corticosterone Release in the Female Rat: Dynamic Interaction with the Response to Acute Stress Endocrinology, February 1, 1998; 139(2): 443 - 450. [Abstract] [Full Text] [PDF]

				R. J. Windle, M. M. Brady, T. Kunanandam, A. P. C. da Costa, B. C. Wilson, M. Harbuz, S. L. Lightman, and C. D. Ingram Reduced Response of the Hypothalamo-Pituitary-Adrenal Axis to {alpha}1-Agonist Stimulation during Lactation Endocrinology, September 1, 1997; 138(9): 3741 - 3748. [Abstract] [Full Text] [PDF]

				H. C. Atkinson and B. J. Waddell Circadian Variation in Basal Plasma Corticosterone and Adrenocorticotropin in the Rat: Sexual Dimorphism and Changes across the Estrous Cycle Endocrinology, September 1, 1997; 138(9): 3842 - 3848. [Abstract] [Full Text] [PDF]