0013-7227/91/1283-1285I03.00/0 Endocrinology Copyright © 1991 by The Endocrine Society
Vol. 128, No. 3 Printed in U.S.A.
Effect of Relaxin on Mammary Development in Ovariectomized Pregnant Gilts* W. L. HURLEY, R. M. DOANE, M. B. O'DAY-BOWMAN, R. J. WINN, L. E. MOJONNIER, AND 0. D. SHERWOOD Departments of Animal Sciences (W.L.H, R.M.D.) and Physiology and Biophysics (M.B.O-B., R.J.W., L.E.M., O.D.S.) and College of Medicine (O.D.S.), University of Illinois, Urbana, Illinois 61801
ABSTRACT. The role of relaxin in mammary development was studied between days 80-110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. To obtain an objective measurement of lobulo-alveolar (parenchymal) composition, mammary glands were cut in cross-section through the teat, and the area of parenchymal tissue on the exposed face of the gland was determined. Ovariectomy on day 80 or 100 followed by progesterone replacement therapy resulted in a dramatic reduction in the rate of growth of mammary parenchymal crosssection area on days 100 and 110 of gestation, respectively, compared to that in controls. In contrast, progesterone plus
A
VARIETY of biological actions have been attributed to the polypeptide hormone relaxin in estrogen-dominated animals (1-3). Most of these actions relate to reproductive function and center around the maintenance of pregnancy and the preparation of the reproductive tract for parturition. Studies conducted with pregnant animals indicated that highly purified relaxin inhibits uterine contractile activity in rats (4), promotes increased growth and softening of the cervix in rats and pigs (5, 6), and promotes increased pelvic area in cattle (7). The effects of relaxin on growth and development of the mammary gland have not been examined during pregnancy in any species and remain poorly understood. Sporadic studies between 1945 and 1977 with estrogenpretreated nonpregnant laboratory animals indicated that partially purified porcine relaxin promotes growth and lobulation of the mammary glands in rats (8-11), guinea pigs (12), rabbits (12), and mice (13). Recent Received September 27,1990. Address all correspondence and requests for reprints to: Dr. O. D. Sherwood, Department of Physiology and Biophysics, University of Illinois, 524 Burrill Hall, 407 South Goodwin Avenue, Urbana, Illinois 61801. * This work was supported by USDA Grant AG-87-CRCR-1-2578 (to O.D.S.), a grant from the National Pork Producers Council (to O.D.S.), Illinois Agricultural Experiment Station Project 35-0370 (to W.L.H.), and a predoctoral fellowship from Systems and Integrative Biology Training Grant GM-07143 (to M.B.O.-B.).
relaxin therapy, with highly purified porcine relaxin, restored the mammary parenchymal cross-section area to control values in ovariectomized gilts. Morphometric analysis of mammary tissue on day 110 of pregnancy indicated that both the absence of relaxin after ovariectomy and replacement therapy with porcine relaxin in ovariectomized gilts had little if any effect on the percentages of the lumen, stroma, or epithelia that comprised the mammary parenchyma. It is concluded that relaxin has a stimulatory effect on the growth of mammary parenchymal tissue during late gestation in the pig. {Endocrinology 128: 1285-1290,1991)
studies employing highly purified porcine relaxin confirmed and extended the earlier findings (14-19). Bani and co-workers (15-19) reported that relaxin enhanced the effects of estrogen on the growth and development of both mammary ducts and stromal tissue in intact or ovariectomized estrogen-primed mice. Pregnancy in the domestic pig extends, on the average, 115 days. In the pregnant pig, the corpora lutea produce relaxin, and the placenta produces estrogen; serum levels of both hormones increase steadily from about day 80 until term (20). Between days 80-100, serum estrogen levels increase about 10-fold, but serum relaxin levels increase far more slowly and remain below 3 ng/ml on day 100. Between days 100-110, serum levels of both estrogen and relaxin increase rapidly, and by day 110, relaxin levels are approximately 12 ng/ml (20). We recently reported that marked and sustained growth and extensibility of the cervix occur between days 80-110 of pregnancy (20), and that relaxin plays a major role in promoting these cervical modifications (6). There is reason to suspect that relaxin, probably in conjunction with estrogen, also promotes growth of the mammary glands in pregnant pigs. As with cervical modifications in primiparous pigs, mammary lobulo-alveolar tissue proliferation begins to occur rapidly about day 80 (21). Moreover, when gilts were ovariectomized on days 60-65 and pregnancy was maintained with progesterone, there was only
1285
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 29 October 2015. at 04:56 For personal use only. No other uses without permission. . All rights reserved.
Endo-1991 Voll28-No3
RELAXIN AND MAMMARY DEVELOPMENT
1286
a small amount of lobulo-alveolar development of the mammary glands on day 100 of pregnancy in spite of normal serum levels of estrogen (22). The present study examined the effects of highly purified porcine relaxin on the development of the mammary gland during the last third of pregnancy in ovariectomized gilts.
Materials and Methods Animals and treatments Forty-eight cross-bred gilts were used for this study. These animals were also used for a study that examined the influence of relaxin on the physical properties of the cervix, and the seven treatments were reported in detail previously (6). The experimental design involved two periods of pregnancy: days 80-100 (when serum relaxin levels are
Vol. 128, No. 3 Printed in U.S.A.
Effect of Relaxin on Mammary Development in Ovariectomized Pregnant Gilts* W. L. HURLEY, R. M. DOANE, M. B. O'DAY-BOWMAN, R. J. WINN, L. E. MOJONNIER, AND 0. D. SHERWOOD Departments of Animal Sciences (W.L.H, R.M.D.) and Physiology and Biophysics (M.B.O-B., R.J.W., L.E.M., O.D.S.) and College of Medicine (O.D.S.), University of Illinois, Urbana, Illinois 61801
ABSTRACT. The role of relaxin in mammary development was studied between days 80-110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. To obtain an objective measurement of lobulo-alveolar (parenchymal) composition, mammary glands were cut in cross-section through the teat, and the area of parenchymal tissue on the exposed face of the gland was determined. Ovariectomy on day 80 or 100 followed by progesterone replacement therapy resulted in a dramatic reduction in the rate of growth of mammary parenchymal crosssection area on days 100 and 110 of gestation, respectively, compared to that in controls. In contrast, progesterone plus
A
VARIETY of biological actions have been attributed to the polypeptide hormone relaxin in estrogen-dominated animals (1-3). Most of these actions relate to reproductive function and center around the maintenance of pregnancy and the preparation of the reproductive tract for parturition. Studies conducted with pregnant animals indicated that highly purified relaxin inhibits uterine contractile activity in rats (4), promotes increased growth and softening of the cervix in rats and pigs (5, 6), and promotes increased pelvic area in cattle (7). The effects of relaxin on growth and development of the mammary gland have not been examined during pregnancy in any species and remain poorly understood. Sporadic studies between 1945 and 1977 with estrogenpretreated nonpregnant laboratory animals indicated that partially purified porcine relaxin promotes growth and lobulation of the mammary glands in rats (8-11), guinea pigs (12), rabbits (12), and mice (13). Recent Received September 27,1990. Address all correspondence and requests for reprints to: Dr. O. D. Sherwood, Department of Physiology and Biophysics, University of Illinois, 524 Burrill Hall, 407 South Goodwin Avenue, Urbana, Illinois 61801. * This work was supported by USDA Grant AG-87-CRCR-1-2578 (to O.D.S.), a grant from the National Pork Producers Council (to O.D.S.), Illinois Agricultural Experiment Station Project 35-0370 (to W.L.H.), and a predoctoral fellowship from Systems and Integrative Biology Training Grant GM-07143 (to M.B.O.-B.).
relaxin therapy, with highly purified porcine relaxin, restored the mammary parenchymal cross-section area to control values in ovariectomized gilts. Morphometric analysis of mammary tissue on day 110 of pregnancy indicated that both the absence of relaxin after ovariectomy and replacement therapy with porcine relaxin in ovariectomized gilts had little if any effect on the percentages of the lumen, stroma, or epithelia that comprised the mammary parenchyma. It is concluded that relaxin has a stimulatory effect on the growth of mammary parenchymal tissue during late gestation in the pig. {Endocrinology 128: 1285-1290,1991)
studies employing highly purified porcine relaxin confirmed and extended the earlier findings (14-19). Bani and co-workers (15-19) reported that relaxin enhanced the effects of estrogen on the growth and development of both mammary ducts and stromal tissue in intact or ovariectomized estrogen-primed mice. Pregnancy in the domestic pig extends, on the average, 115 days. In the pregnant pig, the corpora lutea produce relaxin, and the placenta produces estrogen; serum levels of both hormones increase steadily from about day 80 until term (20). Between days 80-100, serum estrogen levels increase about 10-fold, but serum relaxin levels increase far more slowly and remain below 3 ng/ml on day 100. Between days 100-110, serum levels of both estrogen and relaxin increase rapidly, and by day 110, relaxin levels are approximately 12 ng/ml (20). We recently reported that marked and sustained growth and extensibility of the cervix occur between days 80-110 of pregnancy (20), and that relaxin plays a major role in promoting these cervical modifications (6). There is reason to suspect that relaxin, probably in conjunction with estrogen, also promotes growth of the mammary glands in pregnant pigs. As with cervical modifications in primiparous pigs, mammary lobulo-alveolar tissue proliferation begins to occur rapidly about day 80 (21). Moreover, when gilts were ovariectomized on days 60-65 and pregnancy was maintained with progesterone, there was only
1285
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 29 October 2015. at 04:56 For personal use only. No other uses without permission. . All rights reserved.
Endo-1991 Voll28-No3
RELAXIN AND MAMMARY DEVELOPMENT
1286
a small amount of lobulo-alveolar development of the mammary glands on day 100 of pregnancy in spite of normal serum levels of estrogen (22). The present study examined the effects of highly purified porcine relaxin on the development of the mammary gland during the last third of pregnancy in ovariectomized gilts.
Materials and Methods Animals and treatments Forty-eight cross-bred gilts were used for this study. These animals were also used for a study that examined the influence of relaxin on the physical properties of the cervix, and the seven treatments were reported in detail previously (6). The experimental design involved two periods of pregnancy: days 80-100 (when serum relaxin levels are
