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K Rajkumar

Publications and source records attributed to K Rajkumar.

At least 55 records · Page 3Linked to original sources
PubMed1985

Effect of lipoproteins and luteotrophins on progesterone accumulation by luteal cells from the pregnant pig.

The roles of prolactin (Prl) and LH in the maintenance of luteal function in pregnant pigs were investigated. Luteal cells from pigs between days 70 to 95 of pregnancy were dissociated and incubated for 4 h. In the absence of exogenous cholesterol, LH exhibited a dose-dependent stimulatory effect on progesterone secretion. Prl had a mild stimulatory effect on progesterone accumulation and at lower doses Prl potentiated the response to LH. Low density lipoprotein (LDL) but not high density lipoprotein (HDL) had a mild stimulatory effect on progesterone secretion. When exogenous cholesterol was provided as the substrate in the form of LDL or HDL, Prl had a striking stimulatory effect on progesterone secretion. When 25-hydroxycholesterol which bypasses the lipoprotein receptor was provided as the substrate, Prl failed to stimulate progesterone accumulation. The stimulatory effect of LH was potentiated when LDL, HDL, or 25-hydroxycholesterol were present. The results of this study suggest that LH increases the uptake of exogenous cholesterol in the form of lipoproteins and enhances the utilization of internalized cholesterol for progesterone synthesis. Prl appears to stimulate progesterone synthesis by enhancing the uptake of lipoproteins.

Animals↗
PubMed1985

Binding of high-density lipoproteins to luteal membranes: the role of prolactin, luteinizing hormone, and circulating lipoproteins.

Ovarian and adrenal membranes from immature gonadotropin-primed rats, treated with 4-amino-pyrazolopyrimidine (4APP) to reduce endogenous lipoprotein levels, displayed higher binding of porcine high-density lipoprotein (HDL) when compared to control rats. Immature, hypophysectomized (HYPOX) rats bearing corpora lutea (CL) on Day 5 after ovulation had lower levels of serum progesterone and reduced capacity for HDL and human chorionic gonadotropin (hCG) binding to ovarian membranes when compared with intact animals. Hypophysectomy also reduced the number of HDL binding sites in adrenal membranes. Treatment of HYPOX animals with luteinizing hormone (LH) and prolactin (Prl) alone or in combination increased the HDL binding sites in the ovary relative to HYPOX-untreated rats. Neither hormone affected binding to adrenals, where only adrenocorticotropic hormone (ACTH) enhanced HDL binding. LH treatment reduced the serum progesterone levels and hCG binding to the ovaries, whereas Prl administration increased progesterone levels with no effect on hCG binding. We conclude from this study that HDL binding in the luteinized ovary is regulated by Prl and LH and circulating lipoproteins, whereas in adrenals it is regulated by ACTH and circulating levels of lipoproteins.

Adenine↗
PubMed1985

Prolactin as a luteotrophin.

This review summarizes evidence suggesting a direct luteotrophic role for the hypophyseal hormone prolactin (PRL). This direct role consists of the capability to stimulate progesterone synthesis in vitro, the capability to maintain the membrane fluidity and receptors for luteinizing hormone and the capability to import substrate for progesterone synthesis. The time required for PRL-induced luteotrophic events is in the order of hours and sometimes days, and it appears that the effects are not associated with acute intracellular changes. The relatively slow responses and the stimulation of specific protein synthesis by PRL in target tissues other than the ovary suggest that PRL may function primarily through activation of the genome. PRL may induce the synthesis of specific luteal proteins, including enzymes for the regulation of intracellular substrate pools, membrane receptors for LH, or receptor proteins for lipoproteins, a major extracellular source of substrate.

Animals↗
PubMed1985

The effects of hypophysectomy and administration of pituitary hormones on luteal function and uptake of high density lipoproteins by luteinized ovaries and adrenals of the rat.

The role of plasma lipoproteins and hypophyseal hormones in the maintenance of progesterone secretion by the rat corpus luteum was investigated. In the first experiment, rats were treated daily from days 1-6 of pregnancy with 5 mg/kg 4-aminopyrozolopyramidine (4APP), a blocker of hepatic lipoprotein secretion, or with 5 mg/kg 4APP and 1 or 2 mg ovine PRL or 0.1 ml 0.5% phosphoric acid (4APP vehicle). The administration of 4APP reduced serum cholesterol and progesterone levels on days 2-6 of pregnancy and ovarian progesterone on day 6. The reduced progesterone secretion had no effect on embryo implantation. PRL, in the doses used, was incapable of abrogating the effects of 4APP on circulating or ovarian progesterone levels. Ovaries and adrenals, but not kidneys, of pseudopregnant rats exhibited specific and saturable uptake of porcine high density lipoprotein (HDL). Time-course studies indicated that the uptake of HDL was rapid in ovaries compared to that in adrenals. Ovaries from rats not only exhibited uptake of porcine HDL, but also were capable of using it for progesterone synthesis. Immature rats were assigned to 7 groups of 16 rats each; 8 rats from each group received 4 mg/kg 4APP, and 8 received 4APP vehicle from day 1 of pseudopregnancy. Four groups underwent hypophysectomy on day 1 and received one of the following: 0.1 mg (30 IU/mg) ovine PRL, 0.1 mg ovine LH or 0.1 mg synthetic ACTH daily, or no replacement therapy. Three sham-hypophysectomized groups received 0.1 mg PRL or LH twice daily or no hormone treatment. On day 5 of pseudopregnancy, rats received intravascular HDL, as described above, and were killed 1 h later. Treatment with 4APP increased the adrenal uptake of HDL, but ovarian uptake was not different from that in the control group. Hypophysectomy reduced both adrenal and ovarian uptake of HDL. In adrenals only ACTH at the dose employed ameliorated reduction of HDL uptake induced by hypophysectomy, while in the ovaries, both PRL and LH reversed the effect of hypophysectomy. The effect of PRL on uptake was specific to [125I]HDL and did not alter [125I]albumin uptake. It is concluded that: 1) hypophysectomy reduces HDL uptake in the luteinized rat ovary; and 2) PRL and LH replacement therapy maintain ovarian uptake of HDL, suggesting a direct effect of these luteotropins on lipoprotein uptake.

Adrenal Glands↗
PubMed1984

Role of lipoproteins and prolactin in luteal function in the ferret.

This study investigated luteal function in vitro during early pregnancy and pseudopregnancy in the ferret. Corpora lutea taken from animals on Day 13 following the ovulatory stimulus (mating or gonadotropin treatment) were dissociated with collagenase and incubated with ovine prolactin (Prl), ovine luteinizing hormone (LH), total lipoprotein fraction from canine serum, canine high-density lipoproteins (HDL), canine low-density lipoproteins (LDL) or combinations of Prl, LH, HDL, and LDL. Total lipoproteins produced statistically definable increases in progesterone accumulation in incubation media at 5 microliter (approx. 50 micrograms protein) through 25 microliter (250 micrograms protein) of the total lipoprotein solution. LDL in doses of 1 or more microgram protein stimulated progesterone accumulation in 2-h incubations and a similar stimulation was observed in the presence of 60 or more micrograms HDL. Prl, LH or the combination of Prl and LH had no apparent stimulatory influence on progesterone accumulation in vitro. Prl in combination with LDL further stimulated progesterone output by luteal cells in short-term incubation relative to LDL alone. Prl and LH together with LDL produced an increase in stimulation over LDL alone, but, for the most part, this augmentation did not exceed that recorded in the presence of the combination of Prl and LDL. No interactions between HDL and luteotropic hormones were present. The results indicate that lipoproteins increase progesterone output from ferret luteal cells, presumably by providing substrate for steroid hormone synthesis. No direct role for LH in ferret luteal function emerged from these experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Prostaglandin release by zygotes and endometria of pregnant rabbits.

When 4-day rabbit zygotes were incubated for 1 h at 37 degrees C in vitro, very little prostaglandin (PG) was released into the medium, and the concentration of PGs in the zygotes after incubation was also low. The release of prostaglandin E (PGE) and prostaglandin F (PGF) into the medium, and their concentration in the zygotes after incubation, increased sharply on Days 6 and 7 of pregnancy, reaching, by Day 7, values close to 200 ng of each PG released in 1 h per mg of protein. By contrast, endometrial samples on Days 4 and 5 of pregnancy released more PGF and less PGE than the zygotes of the same ages on a per mg of protein basis, and on Days 6 and 7, less of both PGs. Furthermore, endometrial concentrations of PGs after incubation, except for PGF on Day 4, were always lower than values for zygotes. Endometrial concentrations of PGs on Day 6 were lower before than after incubation. Although there was a slight upward trend in PG release by endometrial samples with increasing length of pregnancy, the changes were minimal and, in the case of PGE, none of the mean values exceeded 1 ng per mg of protein. In 7-day blastocysts, high levels of both PGF and PGE were found in the blastocoelic fluid, and these did not change during the 1-h incubation. The release of PGF and PGE during in vitro incubation of ruptured and washed Day 6 blastocysts was stimulated by arachidonic acid, and that of PGF, but not PGE, inhibited by indomethacin. The release of PGE, but not of PGF, from Day 6 blastocysts was inhibited by low temperature, and the same conditions inhibited release of both PGF and PGE from endometrial cell suspensions. It seems that both blastocysts and endometria have capability to synthesize PGs, the blastocysts being particularly active in this regard on Days 6 and 7 of pregnancy. It is hypothesized that, in vivo, Day 6 and 7 blastocysts release large quantities of PGs which trigger some of the local endometrial changes associated with pregnancy.

Animals↗
PubMed1983

Uteroglobin production by cultured rabbit uterine epithelial cells.

Uteroglobin (UG) is a secretory protein produced by the rabbit endometrium and its production is increased during cell differentiation which occurs during early pregnancy or pseudopregnancy. In the present study, the optimal conditions for UG production by rabbit endometrial epithelial cells in culture were examined. Metabolic labeling studies showed the incorporation of [35S]methionine into UG molecules by the endometrial epithelial cells in culture. Accumulation of UG in culture media was linear for at least a period of 24 h. These cells do not catabolize exogenously added radiolabeled UG. Endometrial cells obtained from virgin female rabbits at different times after the administration of human CG (hCG) and put in culture were found to make different amounts of UG. The maximal UG production was found in cells taken from pseudopregnant rabbits 4 days after hCG administration. Cycloheximide (28 micrograms/ml) inhibited the production of UG by the cells in culture whereas actinomycin-D (5 micrograms/ml) and cordycipin (50 micrograms/ml) increased its production. Inhibition of DNA synthesis by hydroxyurea (10(-3) M) did not affect the UG production. The production of UG was significantly less when cells were cultured on attached or floating collagen gels as compared to cells grown on plastic Petri dishes. The amino acid content of Ham's F-12 medium was shown to be adequate for maximal UG production; lowering this amino acid concentration decreased the amount of UG accumulated in the medium over a 24-h period. Increasint the number of cultured cells per dish resulted in an increased UG production per cell.

Animals↗
PubMed1981

Effects of tension and transmural stimulation on prostaglandin production by estrous rabbit oviductal isthmus.

The effect of longitudinal and circular stretch on the amounts of Prostaglandin F (PGF) and Prostaglandin E (PGE) found in the fluid bathing rabbit oviductal isthmus has been investigated. It was found that the amounts of PGE and PGF measured in the bathing fluid of longitudinally or circularly stretched tissues were negatively correlated to the maturity of the animal. Prostaglandin E increased with time in the tissues under longitudinal and circular tension. Prostaglandin F also increased with time under longitudinal tension but remained fairly constant under circular tension. Increasing the load from 0.5 to 2.0 g had no significant effect on PGE found under longitudinal or circular tension or on PGF found under longitudinal tension. Under circular tension, PGF found increased. Transmural stimulation at 20 Hz increased PGE 8-fold over control values while PGF increased only 1 to 3-fold. It is suggested that distension of the rabbit oviductal isthmus results in increased PGF production, which could be important in ovum transport.

Animals↗
PubMed1981

Fertility and ovum transport after microsurgical removal of the uterotubal junction in rabbits.

The role of the uterotubal junction (UTJ) in fertility and ovum transport was investigated following unilateral microsurgical resection of the UTJ in 15 rabbits. Fourteen animals became pregnant on the UTJ resected side and 14 on the control side following artificial insemination and induction of ovulation. Fifty-two of 61 ova (85.2%) became implanted on the control side, and 56 of 68 ova (82.3%) became implanted on the resected side. Ten days after delivery, artificial insemination and induction of ovulation were repeated. Ovum transport was examined at 60, 66, and 72 hours. There was no significant difference in ovum transport between UTJ resected and control sides. The distribution of ova within the oviduct and the time of their entrance into the uterus was comparable in both sides. These results indicate that the UTJ is not necessary for normal fertility and ovum transport in the rabbit.

Animals↗
PubMed1981

Effect of ovulation on the response of the rabbit oviduct to acetylcholine in vitro.

Acetylcholine had a stimulatory effect on both the longitudinal and circular isthmi of the rabbit fallopian tube in vitro. The longitudinal isthmus was more responsive than the circular isthmus. The stimulatory effect was blocked by phentolamine (3 x 10(-7) M). The oviduct obtained from animals sacrificed 24 h after human chorionic gonadotropin (hCG) administration was more responsive to acetylcholine as compared to the oviduct obtained 72 h after hCG and from animals without ovulation induction. The maximum isometric tension developed was greater in tissues obtained from animals sacrificed 24 h after hCG. The results of this study suggest that the effect of acetylcholine may be partly mediated through the release of noradrenaline and may have a functional role in the regulation of ovum transport.

Acetylcholine↗
PubMed1979

Effect of estradiol and progesterone on the isometric tension developed by longitudinal and circular isthmus of rabbit fallopian tube.

The effect of estradiol and progesterone on the isometric tension developed by longitudinal and circular muscle of isthmus of rabbit fallopian tube to various agonists was studied. The isometric tension developed was reduced by about 50% under progesterone dominance as compared to estrogen dominance. This inhibition was of non-specific nature and did not involve adrenergic receptors. The non-specific effect of progesterone may have a role in regulating the entry of ova into the isthmus after their initial retention at the ampullary--isthmic junction.

Animals↗
PubMed1979

Relationship between concentration of prostaglandins E and F in the regulation of ovum transport in rabbits.

Prostaglandin E and F levels were measured by a radioimmunoassay technique in different parts of the rabbit fallopian tube treated with indomethacin and in untreated rabbit at 0, 24, 48 and 72 hours after Human Chorionic Gonadotrophin (HCG) administration. The results indicate a significant rise in the levels of PGE and fall in the levels of PGF throughout the isthmus at 48 hours and in the distal isthmus at 72 hours in the untreated rabbits. In the indomethacin treated rabbits, PGF levels were reduced relatively more than PGE levels in different parts of the rabbit fallopian tube at various time intervals after HCG administration. Prostaglandins E and F may have a role in regulating ovum transport.

Animals↗