Adaptation of the Kidney During Reproduction: Role of Estrogen in the Regulation of Responsiveness to Parathyroid Hormone

Abstract

Avian kidney function adapts during reproduction to provide the calcium required for eggshell formation. Adaptive changes in kidney function are 1) increased parathyroid hormone (PTH)-dependent adenylate cyclase activity; 2) elevated numbers of PTH receptors; and 3) increased synthesis of 1,25-dihydroxycholecalciferol. Because exogenous estrogen mimics these changes, this study explored the physiological role of estrogen in the regulation of kidney function by altering egg-laying status or levels of estradiol. In hens, treatment with the coccidiostatic drug, nicarbazin, led to cessation of egg laying with maintenance of the reproductive tract and of plasma estradiol and calcium. The PTH-dependent adenylate cyclase activity remained elevated (upregulated). However, when molting was induced by altering the photoperiod and diet, plasma estradiol, plasma calcium, and renal PTH-dependent adenylate cyclase activity all decreased. The depressed responsiveness to PTH was restored by administration of estradiol either during the molt or upon return to egg laying following the molt. When the estrogen antagonist, tamoxifen, was administered to laying hens, reproduction ceased and the PTH-dependent adenylate cyclase activity of renal membranes was decreased. In all three groups of nonlaying birds, the activity of kidney 25-hydroxycholecalciferol-1-hydroxylase was markedly decreased relative to that of laying hens irrespective of the amount of plasma estradiol. It was concluded that estrogen regulates the PTH-dependent adenylate cyclase system of avian kidney, whereas the activity of the 25-hydroxycholecalciferol-1-hydroxylase of kidney and thus, the synthesis of 1,25-hydroxycholecalciferol may be governed at least in part by the regulation of renal receptors for PTH by estrogen.

Calcium Homeostasis in the Laying Hen.

“…Therefore, it may be concluded that plasma Ca levels of laying hens is a strong regulator of this enzymatic system. This conclusion is in agreement with previous reports (Bar et al, 1978;Forte et al, 1983;Armbrecht and Forte, 1985;Martz et al, 1985;Elaroussi et al, 1993).…”

“…During reproductive activity in the female chicken, endogenous estrogen mediates changes in the function of the kidney that involve the two major Caregulating hormones: PTH and 1,25 (OH) 2 D 3 (Elaroussi et al, 1993). The number of PTH receptor sites and the activity of PTH-dependent adenylate cyclase are elevated in the kidney of mature egglaying females, relative to either the mature male or immature chicken of either sex (Forte et al, 1983).…”

Effect of Adding Okra Powder and Vitamin C or E to the Diet on some Qualitative Characteristics and Oxidation Indices in the Eggs of Lohmann Brown-Lite Hens

“…It increases the calcium concentration in the blood serum by stimulating the kidneys to secrete an enzyme (1α-hydroxylase), which works to convert the inactive form of vitamin D (25-hydroxyCholecalcifrol) to form the active form of vitamin D (1.25-dihydroxy Cholecalcifrol) It is important in the absorption of calcium and phosphorous from the mucous membrane of the small intestine through its association with receptors located in the cytoplasm and then its transmission to the nucleus and stimulating the formation of the calcium-binding protein (P. B.Ca), which works to transport and absorb calcium, thus increasing their level in the blood serum. Or, estrogen may stimulate the activity of the enzyme adenylate cyclase in the cell membrane, thus increasing the process of entering the hormone (PTH) Parathormone, which is responsible for regulating calcium and phosphorous levels in the blood and manufacturing the active form of vitamin D, thus increasing its absorption in the duodenum [15][16][17]. Estrogen increases the gene expression of calcitonin in uterine cells to increase the source of calcium deposition processes in the egg shell, [14].…”