Effects of prostaglandins on prolactin and growth hormone synthesis and secretion in cultured rat pituitary cells

The impact of parturition induction with cloprostenol on immunological parameters in the sow colostrum

BACKGROUND

Farrowing induction with prostaglandin F2 analogue cloprostenol is commonly used on commercial farms to manage the timing of farrowing. When labour induction is applied, the questions arise about possible side effects of such a hormonal intervention on physiological processes connected with labour and lactation, including colostral immunity.

RESULTS

In this study, immune cells composition, lysozyme concentration, complement bacteriolytic activity and proinflamatory (GM-CSF2, IL-1β, IL-6, a TNFα) and anti-inflammatory (IL-4, IL-10, TGFβ1 a TGFβ2) cytokines were measured in colostrum samples from sows farrowing naturally (NP) and from sows with farrowing induced using cloprostenol administration on day 113 of gestation (IP). A significantly higher proportion of lymphocytes was found in colostrum of induced sows compared to colostrum of non-induced sows. No significant differences between NP and IP were found in complement activity, in the proportions of granulocytes, macrophages and lymphocyte subpopulations. Lower lysozyme concentration and higher IL-1β, IL-6, TGFβ1 and TNFα concentrations were found in IP sow colostrum compared to colostrum from NP sows.

CONCLUSIONS

An increased proportion of colostral lymphocytes can positively influence the cellular immunity transmission from sow to her offspring. On the other hand, a lower lysozyme concentration can adversely affect newborn's intestinal immunity, as well as changes in cytokine concentrations can have an adverse effect on newborn piglet intestinal epithelium development and its defence function.

Annexin 5 inhibits thyrotropin releasing hormone (TRH) stimulated prolactin release in the primary culture of rat anterior pituitary cells

Annexin 5, a novel calcium-phospholipid binding protein, is thought to be involved in hormone secretion by the anterior pituitary gland. Gonadotropin releasing hormone stimulates annexin 5 synthesis, which, in turn, enhances gonadotoropin secretion. On the other hand, annexin 5 was shown to inhibit prolactin release in vitro. To understand the nature of the opposing effects of annexin 5 on these two major pituitary hormones, the present study examines the inhibitory effect of annexin 5 on prolactin release in relation to thyrotropin stimulating hormone (TRH) using primary cultures of anterior pituitary cells of adult female rats. While recombinant rat annexin 5 was found to have little effect on basal prolactin release, it significantly inhibited TRH-stimulated prolactin release. Addition of specific anti-annexin 5 serum to the culture increased basal prolactin release in a concentration dependent manner, and no further increase in prolactin release was observed following application of TRH in the presence of anti-annexin 5. The enhanced basal prolactin release induced by anti-annexin 5 was reversed by the simultaneous administration of indomethacin, an inhibitor of cyclooxygenase. These results demonstrate that endogenous pituitary annexin 5 exerts an inhibitory effect on prolactin release and suggest that this is attained by suppression of eicosanoid synthesis in vitro.

Mathematical description of the interaction between prostaglandins and calcium

The interpretation of the biological action of prostaglandins is very difficult because the shape of the dose-response curves in different assays is often unusual. Horrobin has attempted to explain these unusual curves by supposing special interactions between Ca and the prostaglandin receptors. This paper gives a mathematical description of his theoretical models. The results of computer simulation based on these models were in good agreement with the reported experimental observations.

Mammotroph autoregulation: intracellular fate of internalized prolactin

As part of a study concerning the mechanism of mammotroph autoregulation, the intracellular fate of [125I]iodo rat PRL, internalized by mammotrophs, was determined by quantitative electron microscope autoradiography. Simple grain density (GD) analysis of mammotroph autoradiograms showed that 5 cellular compartments (plasma membrane, Golgi apparatus, secretory granules, nucleus and mitochondria) were significantly labeled and that the labeling pattern in these compartments changed with time. Inclusion of a 25-fold excess of unlabeled PRL inhibited the binding of radiolabeled hormone to mammotrophs by approximately 85%. At no time were any grains found associated with lysosomes and there was no evidence of degradation of the radiolabeled PRL as judged by SDS-polyacrylamide gel electrophoresis or cold perchloric acid precipitation of cell extracts or media samples. Delivery of internalized PRL to a number of specific intracellular organelles suggests that these organelles may serve in the autoregulation of PRL secretion.

Central administration of prostaglandin E2 facilitates while F2 alpha attenuates acute dependence upon morphine rats

The effects of prostaglandin D2 (PGD2), E2 (PGE2), and F2 alpha (PGF2 alpha) on acute dependence on morphine were investigated. Five mature, male Long-Evans rats were trained to lever press for food reinforcement on a fixed-ratio 30 schedule (FR 30 behavior) and implanted with permanent guide cannulas with the tips of the cannulas in their right lateral brain ventricles. The experimental protocol began with a 45 minute behavioral session and brain infusion (1 microliter/minute of a solution containing 2.3 mM CaCl2 in 0.9% saline, ICV). Fifteen minutes into the session the rats were injected with 7.5 mg morphine/kg (IP). Beginning 2.25 hours later the brain infusion was reinitiated during a second 45 minute behavioral session which was interrupted after 15 minutes to inject 1.0 mg naloxone/kg (IP). In several experiments a dose of PG, which did not in-and-of-itself affect behavior, was added to the infusion medium. Prior to the naloxone injection it was ascertained that the behavioral effects of morphine had dissipated. The injection of naloxone or saline did not alter behavior of the rats while they were being infused with a PG or PG vehicle. Injection of naloxone, 3 hours after the injection of morphine, resulted in a significant suppression of FR 30 behavior (withdrawal). A dose of PGE2, which did not alter the initial suppressant action of morphine, potentiated the naloxone effect. A dose of PGF2 alpha, which likewise did not alter the initial action of morphine, antagonized the naloxone effect. However, a higher dose of PGF2 alpha which enhanced the initial morphine effect, caused an enhanced naloxone effect as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prostaglandin F2 alpha on prolactin secretion in the fowl

The plasma concentration of prolactin in immature cockerels was increased between 10 and 40 min after the intravenous administration of prostaglandin (PG) F2 alpha (200 micrograms/kg body weight). Lower doses had no effect on plasma prolactin concentration. The addition of PGF2 alpha (10(-9) to 10(-6) M) to incubation media had no effect on the basal release of pituitary prolactin but reduced the release of prolactin from pituitary-hypothalamus co-incubations. The addition of noradrenaline (10(-7) M), serotonin (10(-7) M), acetylcholine (10(-6) M) or histamine (10(-6) M) to the co-incubation increased the hypothalamus-induced prolactin release, although these effects were not observed in the presence of 10(-7) M PGF2 alpha. The in vitro release of pituitary prolactin was increased by adding chicken hypothalamic extract in the presence or absence of PGF2 alpha. These results suggest a dual effect on PGF2 alpha of prolactin secretion in the fowl; its stimulation in vivo may result from a peripheral action.

Modulations of prolactin and growth hormone gene expression and chromatin structure in cultured rat pituitary cells

I have measured the effect of hormones and other regulatory factors present in the serum component of the culture medium on the levels of growth hormone and prolactin mRNAs in rat pituitary (GH4) cells. Hybridization of cytoplasmic RNA with growth hormone or prolactin cDNA clones indicate that serum depletion reduces significantly the amount of these two mRNAs. The localization of these two genes in chromatin was also analysed using micrococcal nuclease as a probe. At intermediate levels of digestion (about 10% of the input A260 released into a soluble supernatant S1), the bulk of both growth hormone and prolactin genes are rapidly solubilized by the nuclease and appear in the soluble supernatant S1. Nevertheless, at low levels of digestion (less than 4% of the input A260 released into S1) the growth hormone gene remains exquisitively sensitive to micrococcal nuclease while the sensitivity of the prolactin gene is reduced considerably. When one compares the distribution of growth hormone and prolactin genes in chromatin fractions differing in nuclease sensitivity and derived from cells grown in control medium or in depleted medium, it appears that markedly reduced transcriptional activity of the prolactin gene shows no correlation with altered chromatin structure. On the other hand, the chromatin structure of the growth hormone gene is significantly altered when transcription is markedly reduced.

Effect of prostaglandin inhibition on the prolactin, renin, and aldosterone responses to dopamine antagonism

The possible interactions between the prostaglandin and dopamine systems in the control of prolactin, renin and aldosterone secretion were studied in seven normal subjects. The responses to the dopamine antagonist, metoclopramide (10 mg. i.v.) were studied before and after prostaglandin inhibition with indomethacin (50 mg every 8 hr for 3 doses) while the subjects were in balance on a low sodium (less than 10 meq/day) diet. Urinary prostaglandin E excretion was reduced 61% (p less than 0.05) with indomethacin administration. Plasma renin activity (active and inactive) was not significantly affected by indomethacin treatment. However, the renin activity following metoclopramide tended to rise before, and fall after, indomethacin. Plasma aldosterone increased rapidly after metoclopramide, peaking at ten to fifteen minutes (p less than 0.01). There was no significant difference between the control and indomethacin days. Prolactin increased following metoclopramide, peaking at fifteen to thirty minutes (p less than 0.01). The prolactin response was significantly (p less than 0.05) decreased by indomethacin at four of six time points and the area beneath the response curve was significantly (p less than 0.05) blunted (3048 +/- 132 versus 3882 +/- 146 ng. min/ml). The results suggest that a cyclooxygenase product may modulate the prolactin response to dopamine antagonism. Although the renin response to metoclopramide was altered by indomethacin, the aldosterone response to dopamine antagonism is not medicated by cyclooxygenase products or the renin-angiotension system.

The effects of prostacyclin (PGI2) on prolactin secretion in vitro

Continuously superfused rat anterior pituitary cells were used to study the effects of exogenous prostaglandins (PGs) and thromboxanes (TXs) on the secretion of prolactin (PRL). No change in hormone release was observed upon superfusion with TXB2 (10(-5)M) or the TX synthesis inhibitor, imidazole (1.5 mM). PGs A2, B2, D2, E1, E2, F1 alpha, F2 alpha, and endoperoxide analogs, U-44069 and U-46619, also had no effect on PRL secretion (all at 10(-5)M). In contrast 10(-5)M PGI2 was repeatedly found to stimulate PRL release to a level at least 125% above control, while producing no apparent change in the amount of hormone secreted in response to TRH. Somatostatin (SRIF), at a dose of 10(-6)M, maximally inhibited TRH-induced PRL output, but failed to alter the PRL response to PGI2. These studies indicate that PGI2 may have a direct effect on the anterior pituitary to modify PRL secretion.

Interactions between prostaglandins and calcium: the importance of bell-shaped dose-response curves

Biological responses to PGs show two basic forms of dose/response relationship, plateau and bell-types. Although bell-shaped dose/response curves are well documented their possible occurrence is almost always ignored in the design and interpretation of experiments on PGs and related substances. This may lead to serious errors, several types of which are described. The ignoring of a well-documented phenomenon may take place because there is no accepted hypothesis which attempts to explain the bell-type curves. A hypothesis is proposed which accounts for both plateau and bell type responses. It is developed primarily with respect to PG-calcium interactions but may be applicable to some PG-cyclic nucleotide interactions as well. The model leads to precise predictions which can be experimentally tested in many systems.

Regulation of mammary and adipose tissue lipoprotein lipase and blood triacylglycerol in rats during late pregnancy. Effect of prostaglandins

The effects of several prostaglandins on lipoprotein lipase activity of mammary gland and adipose tissue and serum triacylglycerol were studied during late pregnancy in rats. Prostaglandins were injected twice daily for 2 days before and once on the day of analysis. In rats pregnant 20 days, prostaglandin F(2alpha) (PGF(2alpha)) increased the activity of lipoprotein lipase in mammary gland fourfold, reduced the activity in adipose tissue about 60%, and decreased serum concentration of triacylglycerol 50%. PGF(2alpha) also reduced serum concentration of progesterone 90% and increased that of prolactin fivefold, but had no effect on serum concentrations of either immuno-reactive insulin or 17beta-estradiol. Injections of 13,14-dihydro-15-keto PGF(2alpha), a metabolite of PGF(2alpha), had similar effects in rats pregnant 20 days, whereas prostaglandins E(1) and E(2) did not. In rats pregnant 16 days, PGF(2alpha) did not affect lipoprotein lipase activity in the tissues or the concentration of triacylglycerol and prolactin in serum, although it decreased serum progesterone 80%.2-Br-alpha-ergocryptine prevented the increase in serum prolactin in response to PGF(2alpha), but did not alter the effect of PGF(2alpha) on lipoprotein lipase activity or serum triacylglycerol. Progesterone completely blocked the effects of PGF(2alpha) on lipoprotein lipase activity and serum triacylglycerol and prolactin concentrations. These findings indicate that the changes in lipoprotein lipase activity and serum triacylglycerol in PGF(2alpha)-treated rats are probably related to the inhibitory action of PGF(2alpha) on progesterone secretion. They also suggest that endogenous F prostaglandins may play a role in the regulation of lipoprotein lipase activity in mammary gland and adipose tissue near parturition.

Variations in prolactin and growth hormone production during cellular growth in clonal strains of rat pituitary cells

A permanent, clonal strain of rat pituitary tumor cells (GH3-cells) spontaneously synthesizes and secretes prolactin (rPRL) and growth hormone (rGH) into the culture medium. The rates of hormone production (microng extracellular hormone/mg cell protein/24 hours) and synthesis (vida infra) as well as the rate of [3H]thymidine incorporation into DNA (DNA synthesis) have been studied. During logarithmic growth rPRL and rGH production increased to 160 and 250% of the value at day 2 after plating, while during the plateau phase of cell growth hormone production decreased to initial values. The fluctuations in rPRL production could be fully explained by variations in the rate of rPRL synthesis: [3H]eucine incorporated into rPRL as measured with immunoprecipitation and polyacryl-amide gel electrophoresis. Also the rates of synthesis and production of rGH showed parallel changes during exponential and plateau phase of growth, but this hormone was probably degraded intracellularly. The relative reduction in the rate of synthesis of rPRL and rGH during the plateau of growth corresponded closely to the fall in the rate of DNA synthesis. The reduction in rPRL synthesis could not be explained through an inhibition by extra-cellular rPRL accumulation or by cell to cell interaction occurring in dense cultures. The intracellular concentrations of both hormones were unaltered during logarithmic growth, but rose to 500% for rPRL and 200% for rGH during the plateau phase. In spite of the marked variations in basal rPRL and rGH production the GH3 cultures of different ages were equally able to increase rPRL and decrease rGH production in response to thyrotropin releasing hormone (3 X 10(-7) M) and 17beta-estradiol (10(-8)M).