Biphasic effect of PMSG on lactation in the rat

Flint, DJ

doi:10.1530/jrf.0.0700115

Cited by 1 publication

(2 citation statements)

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“…Prolactin implants also prevented the resumption of oestrous cycles which normally occurred around days 22-24 during extended lactation and there are a num¬ ber of reports which suggest that oestrous cycles may inhibit lactation (Tomogane et al 19766;Bruce, Cofré & Ramirez, 1973;Zamora, Mendoza & Ramirez, 1975;Flint, 1984). For this reason we compared the effects of ovariectomy and progesterone treatment (both of which inhibit oestrous cycles) with the effects of prolactin.…”

Section: Discussionmentioning

confidence: 98%

“…Associated with the decline in mammary gland activity is a reduced serum prolactin concentration (de Greef & van der Schoot, 1983) and a resumption of oestrous cycles. Oestrous cycles have been reported to have a deleterious effect on lactation (Tomogane, Ota, Unno & Yokoyama, 1976a;Flint, 1984) and this may be the reason why oestrous cycles are suspended during lactation in many species. One of the aims of this study was to investigate the effects of the resumption of oestrous cycles on prolonged lactation in the rat.…”

Section: Introductionmentioning

confidence: 99%

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Effects of prolactin, progesterone and ovariectomy on metabolic activities and insulin receptors in the mammary gland and adipose tissue during extended lactation in the rat

Flint¹,

Ra²,

Knight³

1984

Journal of Endocrinology

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Prolactin implants prevented the decline in milk yield and the resumption of oestrous cycles which occurred between days 22 and 28 in untreated lactating rats. Ovariectomy and progesterone implants only partially prevented the decline in milk yield despite preventing the occurrence of oestrous cycles. All three treatments increased total RNA content of the mammary gland compared with controls. In untreated rats there were no changes in mammary DNA content or the number of insulin receptors whereas lipoprotein lipase (LPL) activity decreased significantly during the declining phase of lactation. In contrast, the number of insulin receptors, LPL activity and glucose incorporation into lipid increased in adipose tissue. Prolactin prevented the increase in insulin receptors and lipid synthesis and significantly decreased LPL activity in adipose tissue. Progesterone stimulated LPL activity in the mammary gland and also prevented the increase in lipid synthesis and insulin receptors in adipose tissue but was without effect on LPL activity whereas ovariectomy stimulated LPL activity in the mammary gland but prevented only the increase in the number of insulin receptors in adipose tissue. The results show that raising the serum prolactin concentration can prevent the decline in milk yield during extended lactation and whilst part of this effect may be due to a direct effect on the mammary gland and an indirect effect due to inhibition of oestrous cycles, prolactin may also produce part of its effect on milk synthesis by inhibiting competitive metabolic processes in tissues such as adipose tissue.

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%