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Abstract

The relative importance of GH and prolactin in mammary gland function varies between species with prolactin playing a major role in rodents and GH taking lead role in ruminants. In rodents, however, GH appears to play a vital role in maintaining a high-fat/low volume milk in the absence of prolactin and a similar finding has been demonstrated in goats where prolactin deficiency causes a more modest (15%) decrease in milk yield. Surprisingly GH-deficiency in goats induced no further decline in milk yield whereas exogenous GH or prolactin both stimulated milk output considerably. Although direct effects of prolactin on mammary epithelial cells are well-documented effects of GH are believed to be mediated indirectly via IGF-1 production from the liver. We have been unable to confirm this hypothesis in rats and believe this to be because it is too simplistic. By considering prolactin and GH to be survival factors for the mammary gland we now propose a mechanism by which they interact through the IGF system. Involution of the mammary gland involves apoptosis and, in rats, it is induced by prolactin-deficiency or milk accumulation. Coincidentally with this process mammary epithelial cells synthesize and secrete and IGF binding protein, IGFBP-5. We hypothesize that GH stimulates IGF-1 production, possibly from the mammary parenchyma. IGF-1 then acts as a survival factor for the mammary gland. Prolactin plays an essential role since it suppresses the secretion of IGFBP-5 which would otherwise inhibit IGF-1 action and lead to the induction of cell death.

Consequences of dietary energy source and energy level on energy balance, lactogenic hormones, and lactation curve characteristics of cows after a short or omitted dry period

“…In the current study, plasma IGF-1 was greater in cows of parity 2 than in cows of parity ≥3, which is in line with Miller et al (2006). Insulin-like growth factor 1 plays an important role in cell survival and as an anti-apoptotic factor in mammary tissue, and may, therefore, result in greater cell survival and greater persistency in cows of parity 2 than in cows of parity ≥3 (Flint and Knight, 1997). In contrast, the plasma GH concentration was not different between parity groups in the current study.…”

Neural Cell Behavior and Fuzzy Logic

“…As we indicated in Chapter 2, on the one hand, damage increases expression of motivationally-relevant substances, but on the other hand, these substances reorganize properties of neural tissue and affect the processes of neuronal damage and protection. Such a connection with damage-protection was found for galanin [1437,357] cholecystokinin, leptin [175,176,1031], estradiol, angiotensin II [1051,495], neuropeptide Y [1,232,506], vasopressin [1136], androgens [1388,11,978,934], estrogens [1327,1346], neurotensin [172,506], thyrotropin-releasing hormone [955,1302] and prolactin [392]. Neuropeptides and neurohormones act on motivation and exert a strong effect on the processes of neuronal damage in the same tiny concentrations and with similar time courses.…”

“…Sex hormones, which are in fact multiple growth hormones, intervene in the processes of injury-protection of various brain cells and can disrupt metabolism [392,1174,1327]. The short-term effect of estradiol on neurons is non-protective and excitatory [118], while slower (several hours) actions of estradiol are thought to be protective in nature [1347].…”

“…For example, cholecystokinin, leptin[175,176,1031], estradiol, angiotensin II[1051,495], neuropeptide Y[1,232], vasopressin[1136], androgens[1388,11,978,934], estrogens[1327,1346] and prolactin[392] each exerts a strong effect on the damage-protection processes and they can either ameliorate or exacerbate cell death, depending upon the concentration, level of motivation and location of the tissue.…”

Lactation Performance of Small Ruminants in the Maghreb Region

“…Suppression of prolactin secretion in goats and sheep [19,20] had only partially in sheep lactation. This hormone is at least as important as growth factor in maintaining goat milk yield [21].…”