Local production of prostaglandins in relation to mammary function at the onset of lactation in the goat.

Abstract

SUMMARY1. Arterial and mammary venous concentrations of prostaglandins F. (PGFa), E (PGE) and the PGFa metabolite, 13,14-dihydro-15-oxoPGFa (DHK-PGFe) were studied during late pregnancy and the onset of lactation in conscious goats. Mammary secretion concentrations of PGFa and DHK-PGFa were determined, and mammary blood flow, arterial plasma progesterone concentrations and milk composition were also studied.2. A significant output of PGFa from the mammary gland into mammary venous blood was observed during late pregnancy; this output ceased near term.3. Mammary output of DHK-PGFa into venous blood began about 6 days prepartum, suggesting an increasing capacity of the gland to metabolize PGFa.4. The concentration of PGFa in mammary secretion increased from about 4 days pre-partum, that of DHK-PGFa from about 12 days pre-partum.5. It is concluded that although total mammary output of PGFa decreases during late pregnancy and early lactation, the rate of mammary synthesis of PGFa increases and the PGFa is increasingly secreted into milk and metabolized to DHK-PGFe within the mammary gland.

Parathyroid hormone‐related protein and mammary blood flow in the sheep

“…The PGF2L concentration in carotid arterial and pudendal venous blood plasma samples was measured by liquid-phase radioimmunoassay as described previously (Maule-Walker & Peaker, 1980) 20-2 using an anti-serum with cross-reactivities: PGF2a, 100%; PGF1a, 38%; and other prostaglandins and their metabolites < 0-8 %.…”

“…(PGF2,) was measured in arterial and mammary-venous plasma samples, taken during PTHrP infusion, because there is evidence that this prostaglandin is a local factor that increases mammary blood flow during mastitis (Burvenich & Peeters, 1982). It also appears to be an autocrine/paracrine factor in the mammary gland at parturition (Maule-Walker & Peaker, 1980).…”

Feed‐back control of milk secretion in the goat by a chemical in milk.

“…This shows that local intramammary mechanisms are important in the control of secretion during lactation. Intramammary mechanisms also play important roles in controlling secretion at the onset and cessation of lactation (Fleet & Peaker, 1978;Maule Walker & Peaker, 1980;Peaker, 1980); for instance mammary distension by the accumulated milk is responsible for the arrest of secretion after the complete cessation of lactation in the goat (Peaker, 1980). The inhibition of milk secretion which takes place during lactation after several hours of milk accumulation has been generally assumed to be caused by the physical presence of milk accumulating in, and distending, the mammary gland (e.g.…”

Cortisol and regulation of tight junctions in the mammary gland of the late-pregnant goat

“…Their total calcium content was estimated by adapting the EDTA method described by Davies & White (1962) to smaller volumes. PGF 2a was extracted from samples into peroxide-free diethyl ether in preparation for liquid-phase radioimmunoassay (Maule Walker & Peaker, 1980) using an antiserum with percentage cross reactivities PGF 2a 100, PGF la 38, P G F^O l , PGF 1/? 0-8, PGEjO-2 and PGE 2 02.…”

“…Sodium and potassium concentrations in small volumes of fluid taken from the gland before and after injection were used as indicators of' tightness'. The concentration of endogenous prostaglandin F 2a (PGF 2 J in this fluid was measured because local injection of cloprostenol, an analogue of PGF 2a , into the mammary gland of late-pregnant goats has been shown to produce a change in sodium levels which indicates 'loosening' of tight junctions (Maule Walker & Peaker, 1980). The total calcium concentration was measured because abnormally low levels of extracellular calcium appear to cause mechanical opening of junctions between mammary epithelial cells in culture (Pitelka et al 1983).…”