Transport of oestrone sulphate by the mammary gland in the goat

Abstract

During pregnancy in goats the concentration of endogenous oestrone sulphate in milk increased more than twofold, and that in arterial and mammary venous plasma 10- and 20-fold respectively. The concentration in milk was higher than that in arterial plasma, particularly in lactating goats during mid-gestation. This was partly related to mammary production of oestrone sulphate (or of a closely related steroid which cross-reacted in the radioimmunoassay) since in tracer infusion studies the specific activity of oestrone sulphate in milk was significantly lower than that in arterial or mammary venous plasma. It was also related to the existence of a mechanism within the gland which concentrates oestrone sulphate in milk since when infused close-arterially into the mammary gland of a non-pregnant goat with undetectable levels of the endogenous compound in the circulation, a concentration ratio of 7.4:1.0 was reached for oestrone sulphate in milk:arterial plasma. Tracer kinetic studies showed that mammary extraction of [3H]oestrone sulphate was variable (up to 41.3 +/- 30.6%, mean +/- S.E.M.). During intravenous or close-arterial infusion, radioactivity in arterial and mammary venous plasma at steady state was mainly in the form of [3H]oestrone sulphate (range, 64 +/- 10.6 to 80.2 +/- 5.9% of total radioactivity in plasma). The remainder was in the form of compounds chromatographically similar to oestradiol-17 beta-3-monosulphate, oestradiol-17 alpha-3-monosulphate and unconjugated oestrogens. The distribution of radioactivity between these different steriods was similar in arterial mammary venous plasma indicating a low level of selective mammary metabolism or extraction. The amount of labelled oestrone sulphate transferred into milk was low, and it was significantly less in pregnant (range, 0.11 +/- 0.07 to 0.27 +/- 0.16% of total infusate) than in non-pregnant animals (3.23 +/- 0.50%). Studies of the rate of transfer of [3H]oestrone sulphate from blood to milk indicated the presence of a transcellular route with peak activity in milk occurring about 110 min after the start of the infusion.

Oestrone sulphate, adipose tissue, and breast cancer

“…Although oestrone sulphate has been reported to be present in the milk of domestic animals (8,30), derived, at least in the goat, by both production and concentration in the mammary gland (30), the levels detected in commercially available samples of milk and cream were low and similar in magnitude to those found in the plasmas from postmenopausal women (Figure 1). The levels of the non-conjugated oestrone and oestradiol, which might be formed upon metabolism of the conjugate in milk, were also low.…”

Cold Exposure and Mammary Exchanges of Circulating Thyroxine and Oestrone Sulphate in the Goat

“…Sulphoconjugated steroids remaining in the sample were hydrolysed with sulphatase, oestrogens extracted with diethyl ether and the oestrone content assayed (Heap et al 1984). …”

“…Oestrone isolated from the conjugated steroid fraction was identified by thin layer chromatography, and its concentration estimated by radioimmunoassay as described by Heap et al (1984) except for the use of an antiserum (Steranti Research Ltd, St Albans, Herts, product EOOI) which had cross reactivities to oestrone (100%), 17fi-oestradiol (1 4%), oestriol, dehydroepiandrosterone, androstenedione, testosterone, progesterone, 17-hydroxyprogesterone, cortisol and aldosterone (< 030%). Sensitivity of the assay to oestrone sulphate was 2-5 pg/tube and to oestrone 1 8 pg/tube, and intra-and inter-assay coefficients of variation were respectively 3-8% and 9.6% in the estimation of oestrone sulphate and 2.5% and 6 0% in the estimation of oestrone.…”

“…The oestrone sulphate content of milk is used as an early indicator of pregnancy (Heap et al 1984) and it remains to be seen whether maternal cold exposure is a source of variation of this measure.…”

“…Since cold exposure is reported to increase the secretion of thyroxine in cattle (Premachandra, Pipes & Turner, 1958), mammary uptake of thyroxine has been measured in lactating goats in a cold environment. Moreover, because in mid-and late-pregnant lactating goats, the mammary gland absorbs 3H-labelled oestrone sulphate from the circulation and simultaneously releases unlabelled oestrone sulphate, particularly into the milk (Heap, Hamon & Fleet, 1984), we have also examined the effect of cold exposure on the net exchange between gland and circulation of this hormone.…”