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Biomedical subjects

L M Houdebine

Publications and source records attributed to L M Houdebine.

At least 91 records · Page 5Linked to original sources
PubMed1989

Comparison of insulin-like growth factor 1 and insulin effects on prolactin-induced lactogenesis in the rabbit mammary gland in vitro.

In organ culture of pregnant rabbit mammary gland, a low casein synthesis occurs with prolactin (PRL) alone. Insulin markedly potentiates the effect of PRL. Only pharmacological concentrations of insulin (5 micrograms/ml) exert the maximal enhancement, suggesting a possible interaction with the insulin-like growth factor 1 (IGF1) receptor. The presence of IGF1 and insulin binding sites was analyzed and the biological effects of both peptides were compared. Binding of iodinated human IGF1 or porcine insulin to mammary microsomes prepared from mid-pregnant rabbits revealed distinct high affinity binding sites for both peptides (Kd approximately 2 nM). In rabbit mammary explants, we confirmed that only non-physiological concentrations of insulin (greater than or equal to 100 ng/ml) exerted a significant stimulation of the PRL effect. Surprisingly, IGF1 was not found to be more potent than insulin on a molar basis, which did not provide evidence for the exclusive involvement of the IGF1 receptor. Near-physiological concentrations of IGF1 (approximately 100 ng/ml), however, exerted a significant enhancement which suggested a possible action for IGF1 on PRL-induced lactogenesis in vivo.

Animals↗
PubMed1989

[Evidence for a stimulating factor of prolactin and growth hormone secretion present in brewery draff].

Aquous extracts of brewery draff injected intravenously into ewes and cows induced prolactin and growth hormone (GH) secretion. The same draff added to the feed of cows appeared to be unable to significantly stimulate the blood level of prolactin and GH. In these experimental conditions, milk production was not enhanced by draff. Pure beta-glucan extracted from barley also stimulated hormone secretion when administered by the intravenous route. Barley, bier and draff therefore contain a beta-glucan-like factor which stimulates lactogenic hormone secretion. The amount present in draff is probably unable to cause an increase in hormones when administered orally. Hence, the well-established stimulatory effect of draff on milk production results from their nutritive value rather than from their ability of modulating the endocrine system.

Administration, Oral↗
PubMed1988

Effect of pectic substances on prolactin and growth hormone secretion in the ewe and on the induction of casein synthesis in the rat.

Pectins from apple, citrus and sugar beet injected intravenously to ewes markedly stimulated blood prolactin, growth hormone (GH) and cortisol. Pectic acid and polygalacturonic acid exhibited the same property. A preparation of oligogalacturonic acid with a polymerisation degree of 12 to 13 was also active, whereas oligomers with a smaller degree of polymerisation (congruent to 10) were devoid of activity. Pectic acid administered orally to mature virgin rats induced the accumulation of beta-casein in mammary gland. Pectins and some of their derivatives therefore had a lactogenic property and their effect probably resulted from a capacity to trigger lactogenic hormone secretion.

Administration, Oral↗
PubMed1988

Recent data on the structure of rabbit milk protein genes and on the mechanism of the hormonal control of their expression.

Mammary explants or isolated mammary cells from rabbit have been cultured in the presence of insulin, prolactin and cortisol alone or in combination. The cellular content in alpha s1-casein, beta-casein and whey acidic protein (WAP) mRNA have been evaluated using the corresponding cDNA as probes. In all cases alpha s1-casein mRNA was the most abundant and WAP mRNA the least abundant mRNA. The three genes showed essentially similar dependency towards hormones. Prolactin stimulated mRNA accumulation and insulin and cortisol amplified this stimulation. The induction by prolactin was rapid whereas stimulation by insulin was slower. Fragments of rabbit genomic DNA inserted in lambda phage and containing alpha s1-casein, and WAP genes have been cloned. The primary sequence around the CAP site of the three genes has been established. A comparison of the sequences located upstream from the CAP site shows several striking homologies with the corresponding genes from cow, rat and guinea-pig. This suggests that these sequences participate in the transcriptional control of the genes by hormones. The mechanism involved in the transduction of the prolactin message to milk protein genes in unknown. Using mammary explants in culture, several classical mechanisms of transduction have been examined. Phorbol ester, phorbol -12, 13-dibutyrate (PdiBu) inhibited prolactin action. However, another tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), did not alter prolactin action. Kinase C inhibitor H7 did not prevent prolactin action and did not overcome the inhibition by PdiBu. Kinase C is therefore not essential for the transduction of the prolactin message to milk protein gene. Neomycin, which inhibits phosphatidylinositol hydrolysis by phosphorylase C, prevented prolactin action, whereas other inhibitors of phosphatidylinositol metabolism remained uneffective. Degradation of phosphatidylinositol is therefore likely not an essential step of prolactin action on milk protein genes. Inhibitors of tyrosine kinase and phosphatase exhibited a poor capacity to modify the prolactin response. Hence, transduction mechanisms using tyrosine kinase activity likely cannot account for prolactin action.

Animals↗
PubMed1988

Identification of the lactogenic compound present in beer.

Lyophylized beer and extracts of plants used to prepare beer have been administered orally to mature virgin rats and intravenously to ewe. After four days of treatment, beta-casein estimated by a radioimmunoassay was present in the mammary glands of the rats to which beer or barley extracts were given. Injections of lyophilised beer, barley or malt extracts triggered the release of prolactin in ewe whereas hop extracts were inactive. The active compound present in beer barley and malt, was insolubilized in 50% ethanol and it is in the aqueous phase in chloroform extraction. The active preparation contained essentially polysaccharides. This suggests that the lactogenic principle belongs to this class of macromolecule.

Animals↗
PubMed1987

Antiprogesterone and antiglucocorticoid actions of RU 486 on rabbit mammary gland explant cultures. Evidence for a persistent inhibitory action of residual progesterone upon the mammary tissue.

The antiprogesterone and antiglucocorticoid compound RU 486 added to pregnant rabbit mammary gland explant cultures had no effect alone but significantly stimulated casein production in the presence of ovine prolactin (PRL) in a dose dependent manner. This stimulation was inhibited by progesterone (Pg) and the Pg agonist R5020. When the explants were cultured for 5 days with two changes of medium, to eliminate all steroids, and hormones added afterwards, the effect of PRL was potentiated, Pg was no longer inhibitory and RU 486 had no effect, RU 486 also could inhibit the stimulatory action of glucocorticoids added to the cultures along with PRL. The compound was able to displace [3H]dexamethasone and [3H]R 5020 from mammary gland glucocorticoid and Pg receptors respectively and proved to have a high relative binding affinity (RBA) for both receptors when compared with typical ligands for each receptor. The RBAs of RU 486 and the steroids used in this study to mammary gland glucocorticoid and Pg receptors correlated well with the ability of RU 486 to block their biological activities. These results demonstrate that RU 486 has both antiglucocorticoid and antiprogesterone activities in pregnant rabbit mammary glands as well as the existence of a strong inhibitory residual action of Pg in the gland that persists during the first 48 h of culture and that can be eliminated by RU 486 or after several days of culture with no hormones.

Animals↗
PubMed1987

Binding and action of glucocorticoids and mineralocorticoids in rabbit mammary gland. Exclusive participation of glucocorticoid type II receptors for stimulation of casein synthesis.

In order to ascertain whether the effect of corticoids upon casein synthesis in pregnant rabbit mammary gland culture is due to interactions with classical glucocorticoid or type I (mineralocorticoid) receptors we have demonstrated the existence of both types of receptors in the tissue and have studied the effects of aldosterone and the specific glucocorticoid agonist RU 28362 upon casein synthesis in tissue culture. Both compounds significantly stimulated prolactin-induced casein synthesis. On dose-response studies RU 28362 proved to be as active as dexamethasone, cortisol was active at intermediate concentrations and aldosterone was the least active. The three glucocorticoids were able to stimulate DNA synthesis in the tissue, but aldosterone had no effect. Finally, RU 486, a potent glucocorticoid antagonist, blocked the action of aldosterone and the other corticoids upon casein synthesis, whereas spironolactone, a mineralocorticoid antagonist, was unable to do so. These results demonstrate that the stimulatory effect of corticoids upon casein synthesis in pregnant rabbit mammary tissue culture is mediated through classical (type II) glucocorticoid receptors. Transferrin accumulation in the tissue was not modified by any treatment, indicating that the action of the steroids was specific for casein, and not a general stimulation of protein synthesis.

Aldosterone↗
PubMed1987

Effect of tubulozole, a new synthetic microtubule inhibitor, on the induction of casein gene expression by prolactin.

Colchicine and related drugs are known to inhibit milk secretion. They are also able to prevent stimulation of casein and DNA synthesis by prolactin in the mammary gland. The present report reports data obtained with tubulozole, a new antimitotic drug. Tubulozole C added to culture medium of isolated rabbit epithelial mammary cells strongly inhibited their multiplication. Simultaneously, at a concentration of 1 microM, it prevented almost completely the induction of beta-casein mRNA. Induced cells were rapidly deinduced by addition of the drug to the medium. A similar inhibition was observed when the induction was obtained with prolactin alone or with its two stimulators insulin and glucocorticoids. Tubulozole T, an isomer of tubulozole C which is known to be ineffective in disrupting microtubules, did not alter prolactin actions. These data and those obtained with other tubulin-binding drugs strongly suggest that the integrity of microtubules is required for prolactin to deliver its message to the mammary cell.

Animals↗
PubMed1987

Effects of estramustine, a new anti-microtubule drug, on the induction of casein gene expression by prolactin.

Estramustine, a new anti-microtubule drug, was added to the culture medium of rabbit mammary explants with lactogenic hormones. In the absence of the drug, prolactin with insulin and cortisol stimulated DNA synthesis and it induced beta-casein and beta-casein mRNA accumulation in the tissue. As opposed to other anti-microtubule agents such as colchicine, estramustine was unable to prevent prolactin actions. An examination of the mammary cells by immunofluorescence revealed that the microtubule network was significantly altered under the influence of estramustine. These data indicate that the integrity of microtubules is not required for prolactin to deliver its message to the mammary cell. These data also suggest that other anti-microtubule drugs such as colchicine which prevent prolactin action act through their binding to tubulin molecule unrelated to microtubule structures.

Animals↗
PubMed1987

Measurement by radioimmunoassay of casein content in rabbit mammary gland during pregnancy and after prolactin stimulation in organ culture.

A specific homologous radioimmunoassay was developed to measure rabbit beta-casein in rabbit mammary gland with a sensitivity of 0.5 ng/ml protein. It was used to measure casein concentration during pregnancy and in organ culture of mammary gland explants. Casein was detectable in virgin mammary glands, showed a small increase during the first half of pregnancy, increased more than 20-fold between Days 21 and 27, and diminished somewhat on the first days of lactation. After 24 hr of culture, mammary gland explants had no detectable casein, but the addition of increasing concentrations of prolactin to a culture medium which contained insulin (5 micrograms/ml) and cortisol (0.5 microgram/ml) induced a regular increase in the casein content of the tissue. Casein started to increase when 10 ng/ml of prolactin was present and maximal values were achieved for 100 ng/ml of the hormone.

Animals↗
PubMed1985

Plasma and pituitary prolactin levels in rainbow trout during adaptation to different salinities.

The development of a highly specific radioimmunoassay for salmonid prolactin (PRL) using chinook salmon PRL allowed us to study plasma and pituitary PRL profiles in large sedentary rainbow trout (Salmo gairdneri) transferred from fresh water to seawater and vice versa. Plasma osmotic pressure and chloride levels were also measured for 3 weeks following change of salinity. Within 1 day after transfer to full seawater we observed a plasma PRL decrease, which stayed significantly lower (3-5 ng/ml) than the fresh water control group (10-15 ng/ml) during the entire experiment. Pituitary PRL content showed an initial abrupt increase, but after 3 weeks in seawater pituitary PRL content had decreased to the same level as in the fresh water control group. On the contrary, transfer from seawater to fresh water was followed within 1 day by a rise in plasma PRL levels, which stayed high (10-15 ng/ml) after 3 weeks in fresh water. Simultaneously, pituitary PRL content decreased significantly. These results may indicate an important role of PRL in fresh water adaptation of sedentary rainbow trout.

Acclimatization↗