Biomedical subjects

H Papkoff

Publications and source records attributed to H Papkoff.

At least 37 records · Page 2Linked to original sources

PubMed1988

Short and long phases of progesterone secretion during the oestrous cycle of the African elephant (Loxodonta africana).

Serum samples were collected from 3 mature female African elephants once each week for 15-18 months. Circulating concentrations of progesterone, oestradiol and LH were determined by radioimmunoassay (RIA). The LH RIA was validated by demonstrating parallel cross-reaction with partly purified elephant LH pituitary fractions. Changing serum progesterone concentrations indicated an oestrous cycle length of 13.3 +/- 1.3 weeks (n = 11). The presumed luteal phase, characterized by elevated serum progesterone values, was 9.1 +/- 1.1 weeks (n = 11). Two abbreviated phases of progesterone in serum lasting 2-3 weeks were observed in 2 elephants, indicating short luteal phases. Oestradiol concentrations in serum were variable, with no clear pattern of secretion. More frequent blood samples were collected during periovulatory periods and 9 distinct LH peaks were detected; all were followed by rises in serum progesterone concentrations. Periovulatory changes in progesterone and LH in sera correlated with external signs of oestrus and mating behaviour.

Animals↗

PubMed1987

Characterization of a monoclonal antibody which detects luteinizing hormone from diverse mammalian species.

The present study describes the development and characterization of a monoclonal antibody (518B7) generated against bovine LH (bLH). Although 518B7 was extremely specific for LH, very low species specificity was observed. A RIA using this antibody and radioiodinated equine LH (eLH) showed good sensitivity for all mammalian LH preparations tested, with the exception of human LH (15%, relative to the eLH reference standard). Activities of most mammalian LH's ranged between approximately 50-200%. Much less activity was detected with reptilian LH (less than 1.5%). Amphibian and avian LH fractions were essentially inactive. The reactivities of LH alpha and beta subunits from a variety of mammals clearly showed that the antibody reacts with the beta subunit. Sensitive RIAs were also developed utilizing 125I-bovine and 125I-rat LH. Interestingly, all hormone preparations which showed sufficient reactivity for statistical analysis within the dose ranges used in the present study (0.01-1000 ng/tube) produced a displacement curve parallel to the reference standard. We have also validated the use of 518B7 in detecting LH in serum. Parallel dilution curves relative to purified LH reference standards were observed with equine and bovine serum samples and equine pituitary extract. High (average 94%) recoveries were also seen with bovine serum with known amounts of exogenously added bLH. Similar patterns of LH secretion were detected with a RIA based upon 125I-bLH and 518B7 and a previously described polyclonal antibody-based RIA in bovine serum samples during estrus. Thus, a monoclonal antibody for LH has been produced which can be used to develop sensitive and specific RIAs in many different mammalian species.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Characterization of equine luteinizing hormone by chromatofocusing.

Three equine luteinizing hormone (LH) preparations (eLH-A, -B, and -C) recently have been isolated in our laboratory and were shown to differ in average basicity (eLH-A greater than -B greater than -C). The present study further characterizes these preparations by chromatofocusing. Each of these preparations are comprised of a family of isohormones, with 5 major immunoreactive peaks in the pH range of 7 to 4 (approx. pIs = 6.6, 6.1, 5.7, 5.2, and 4.8), with varying amounts of material eluting to either side of the pH gradient. Although similar isoforms are seen in all three LH preparations, the relative proportions of different isoforms vary in a manner reflecting the average charge properties of eLH-A, -B, and -C. While eLH-A contains predominantly basic forms, eLH-C consists largely of acidic material, and eLH-B is composed mostly of isohormones with pIs intermediate to eLH-A and -C. Chromatofocusing of a crude extract from a single horse pituitary gland revealed isohormone peaks corresponding to those found in the highly purified LH preparations. Peak fractions of the various isoforms were used to generate a variety of activity ratios (LH bioactivity:LH radioimmunoassay (RIA), LH radioreceptorassay (RRA):LH RIA, LH bioactivity:LH RRA, follicle-stimulating hormone (FSH) RRA:LH RIA, and FSH RRA:LH RRA activity ratios). The LH bioactivity:LH receptor binding potency ratio showed a linear increase with increasing isohormone acidity (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Inhibition of follicle-stimulating hormone-induced ovulation by indomethacin in the perfused rat ovary.

In isolated, perfused ovaries of rats treated with pregnant mare's serum gonadotropin (PMSG), purified preparations of ovine follicle-stimulating hormone (FSH) (oFSH-211B) and rat FSH (rFSH-I-6), 100 ng/ml, were found to induce ovulations (4.8 +/- 0.9, n = 4, and 6.4 +/- 2.0, n = 5, ovulations per ovary, respectively). Indomethacin (5 micrograms/ml) added to the perfusate inhibited this ovulatory effect and exogenous prostaglandin F2 alpha (PGF2 alpha) (1 microgram/ml), or prostaglandin E2 (PGE2) (0.5 microgram/ml), reversed the blockade. Ovine FSH and rFSH had only a weak stimulatory effect on estradiol release, and only rFSH caused a significant increase in progesterone accumulation. Indomethacin reduced the stimulatory effect of rFSH on progesterone release, and this effect was reversed by PGE2 but not by PGF2 alpha. In a 6-h incubation experiment with preovulatory rat follicles, we tested the biological activity of gonadotropins used to induce oocyte maturation. The concentration of FSH used in the perfusion experiments induced oocyte maturation in more than 88% of the oocytes studied. The data confirm earlier findings that FSH can induce ovulations and show that prostaglandins are involved in this process. The data also indicate that prostaglandins might be involved in the FSH-induced increase of progesterone levels.

Animals↗

PubMed1987

Biological and immunological properties of zebra pituitary gonadotropins: comparison with horse and donkey gonadotropins.

Previous studies from this laboratory have described the properties of purified luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from horse and donkey anterior pituitary glands. The present study afforded the opportunity to further characterize these previously purified hormone preparations and to compare them with enriched gonadotropin fractions from zebra pituitary glands. Although a single LH and FSH fraction was usually obtained for each pool of pituitaries, two separate zebra LH and two donkey FSH preparations were generated. Purified hormone preparations from the horse were designated eLH and eFSH. Preparations zLH-A, zLH-B, and zFSH were obtained from zebra pituitaries, and fractions dLH, dFSH-A, and dFSH-B were prepared from donkey pituitary glands. These preparations were analyzed by LH and FSH radioimmunoassays (RIAs), radioreceptor assays (RRAs), LH bioassay, and chromatofocusing. Clear immunological differences were observed between equid gonadotropins. Homologous RIAs for eLH and eFSH did not cross-react similarly, or in a parallel fashion, with gonadotropins from the donkey and zebra. In contrast, RIAs capable of assessing LH or FSH in a wide number of species showed all equid gonadotropin preparations to have considerable activity and to produce parallel dilution curves. Relative to eLH (1.00), zLH-A was found to have higher LH bioactivity:LH RIA (2.50), LH RRA:LH RIA (1.42), and LH bioactivity: LH RRA (2.21) activity ratios. The dLH and zLH-B fractions only differed from eLH in LH RRA:LH RIA activity (0.69 and 0.62, respectively). Only LH from the horse possessed clear intrinsic FSH-receptor-binding activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Conformation of sturgeon pituitary somatotropin.

Pituitary somatotropin (growth hormone) from the sturgeon (Acipenser gulden-stadti) has been studied by zero-order and second-order absorption spectroscopy, as well as by circular dichroism. Difference absorption spectra have also been generated during proteolytic digestion of the hormone. The molar extinction coefficient of the native protein was found to be 15,000 +/- 110 M-1 cm-1 at 278.5 nm. Comparison of the conformations of sturgeon somatotropin and somatotropins isolated from several mammalian species, including bovine and human, indicates a close relationship between these molecules. Such similarities may be related to the relatively high biopotency of this fish hormone in mammalian assay systems.

Animals↗

PubMed1986

Isolation and characterization of three forms of luteinizing hormone from the pituitary gland of the horse.

Three isoforms of equine luteinizing hormone (eLH-A, eLH-B and eLH-C) have been isolated from horse pituitary glands. Separation was achieved on the basis of charge heterogeneity by ion-exchange chromatography. These charge differences were apparent after final purification, as determined by electrophoretic mobility on polyacrylamide disc gels (RF = 0.14, 0.19 and 0.26 for eLH-A, -B and -C, respectively). Apparent size differences were also noted between the isohormones by gel filtration on Sephadex G-100. Ve/Vo ratios for eLH-A, -B and -C were 1.72, 1.54 and 1.47, respectively. All 3 isoforms were found to contain an equivalent amount of hexose (9.0-9.2%). Isohormones eLH-B and eLH-C, however, possess more sialic acid than eLH-A (6.6-6.7%, vs. 4.5%). The eLH-A and eLH-B preparations contain a similar amount of hexosamine, which is slightly lower than the amount of eLH-C (8.8-9.1% vs. 11.2%). No differences were noted between the isohormones by rat Leydig cell LH bioassay, equine testis LH radioreceptor assay (RRA) or calf testis follicle-stimulating hormone (FSH) RRA. Slight, but nonsignificant, variations were noted between preparations in an eLH radioimmunoassay (RIA). Although chemical variations were detected between the eLH isoforms, no significant differences were observed in in vitro biological and immunological activities. The differences detected in sialic acid content raises the possibility that differences in in vivo clearance rates may exist.

Animals↗

PubMed1986

Properties of equine luteinizing hormone alpha subunit alone and in combination with various beta subunits.

Previous studies have shown that equine luteinizing hormone (eLH) inhibits production of cyclic adenosine monophosphate (cAMP) induced by follicle-stimulating hormone (FSH) in preparations of seminiferous tubules from immature rats. It was also shown that the inhibitory effect was a function of the equine LH (eLH) alpha subunit. To explore this phenomenon further, the intrinsic FSH-like activities of eLH alpha alone and in combination with ovine (o) LH beta, ovine FSH beta, and equine FSH beta were evaluated in several assay systems. In a radioreceptor assay employing 125I-o-FSH and testis membranes from day-old calves, eLH was twice as active as oFSH, eLH alpha was 6% as active as oFSH, and other subunits showed a lack of activity (less than 1.5%). Whereas oLH was only 0.1% as active as oFSH, the hybrid eLH alpha-oLH beta was 3.0% as active. The binding activity of eLH alpha-FSH beta hybrids tended to be higher than the oFSH alpha-FSH beta hybrids. In the cAMP production assay, eLH alpha-FSH beta hybrids exhibited dampened dose-response curves when compared to the oFSH alpha-FSH beta hybrids. In a plasminogen activator assay (PAA) employing granulosa cells from intact 21-24-day-old female rats primed with diethylstilbestrol, eLH had activity comparable to that of oFSH, while eLH alpha was inactive. When eLH alpha was recombined with oFSH beta, eFSH beta, or oLH beta, the PAA stimulatory activity was not altered compared to that of the hybrids oLH alpha-oFSH beta, oFSH alpha-eFSH beta, and the recombinant oLH alpha-oLH beta, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Purification and characterization of equine relaxin.

It has been previously determined that the equine placenta is the sole significant source of relaxin during pregnancy and that relaxin immunoactivity is also present in term placentas. Therefore, placentas obtained at the time of foaling were selected for starting material for purification of equine relaxin. Frozen whole placentas were ground and then extracted with 0.5 N HCl-85% acetone. Relaxin was precipitated by raising the acetone concentration to 97%. Equine relaxin was further purified by stepwise elution ion exchange, gel filtration, and gradient elution ion exchange chromatographies and trichloroacetic acid precipitation. Equine relaxin purified in this manner was shown to be heterogeneous with one major form (R-1) and several minor forms (two of which are identified as R-2 and R-3). About 1.5 mg R-1 were obtained per kg placenta. Purity was assessed by slab and disc gel electrophoresis and dansyl end group analysis. R-1 had a potency of 28 U/mg, as measured in the mouse inter-pubic ligament bioassay and displayed a dose-response curve parallel with porcine relaxin. Amino acid analysis indicated the presence of tyrosine, histidine, and proline, amino acids absent in porcine relaxin. Dansyl end group analysis indicated the blockage of N-terminal groups on R-1 and the presence of Lys on R-3. A lower molecular weight was indicated by the electrophoretic migration of relaxin reduced with 2-mercaptoethanol suggesting that equine relaxin consists of two chains.

Adnexa Uteri↗

PubMed1986

Histamine and increased ovarian blood flow mediate LH-induced superovulation in the cyclic hamster.

Constant infusion of LH (400 micrograms NIH-S24) through an osmotic minipump inserted on Day 1 (oestrus) of the cycle in the hamster resulted in spontaneous superovulation (approximately equal to 29 ova) at the next expected oestrus, increased blood flow (P less than 0.001) to the ovary on Day 3, and slight depletion (0.1 greater than P greater than 0.05) of histamine in the ovary. Treatment with antihistamine (alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, or cimetidine, an H2 blocker) by injections or by infusion using separate osmotic minipumps significantly (P less than 0.01) reduced the number of ova shed in the LH-treated hamsters. Infusion of LH with alpha-fluoromethylhistidine in the same osmotic minipump reduced the bioactivity of the LH. Infusion of antihistamine alone did not alter the normal number of ova shed. The results suggest that the LH-induced superovulation involves stimulation of histamine release; the histamine than may increase ovarian blood flow thus allowing more gonadotrophins to reach the ovary.

Animals↗

PubMed1986

Deglycosylation of gonadotropins with an endoglycosidase.

A commercially available endoglycosidase (N-glycanase, Genzyme, Boston, Mass.) purified from Flavobacterium meningosepticum with a specificity for cleaving asparagine-linked carbohydrate moieties in glycoproteins was tested on several pituitary and chorionic gonadotropins as substrates. All intact hormones tested were resistant to the action of the enzyme as were all beta subunits from the respective gonadotropins. All alpha subunits, however, were susceptible to the enzyme as evidenced by a decrease in molecular size when examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Preparative experiments with ovine luteinizing hormone subunit (oLH alpha) indicated that only 35-40% of the carbohydrate was removed after N-glycanase treatment, suggesting that perhaps only one of the two carbohydrate moieties was cleavable under the conditions employed. The enzyme-modified subunit (DG-oLH alpha) was able to recombine with untreated oLH beta. An in vitro steroidogenic bioassay (rat Leydig cell) showed that the recombinant (DG-oLH alpha-oLH beta) was about 22% as potent as the native oLH, but in a testicular membrane binding assay for LH, it was equal in potency to the native hormone in competing with the radioligand.

Animals↗

PubMed1986

Purification of monkey prolactin from culture medium: biochemical and immunological characterization.

Serum-free culture medium, previously incubated with dispersed monkey pituitary cells, provided a relatively uncontaminated source for extraction and purification of 15 mg of monkey prolactin. N-terminal group analysis of this preparation, M21GB, produced predominantly leucine. The amino acid composition closely resembles that of both human and sheep prolactin. M21GB monkey prolactin migrates in 10% polyacrylamide with sodium dodecyl sulfate (SDS) as a single band with a molecular weight of about 23,000. Multiple bands typical of prolactins are seen with nondenaturing polyacrylamide disc electrophoresis. M21GB contains less than 1% growth hormone, incorporates radioactive iodine with a specific activity of 15 microCi/micrograms and specifically binds to the anti-human prolactin serum-3 provided by the National Hormone and Pituitary Program (B spec/total = 23%). M21GB does not compete in a linear fashion with iodinated human prolactin-16 for the human prolactin antiserum, but M21GB does compete in a linear fashion with iodinated M21GB with the same antiserum. Monkey serum, pituitary homogenate, and culture medium containing unknown levels of monkey prolactin are not parallel with NIAMDD-HPrl-RP1 in the human prolactin assay, but are parallel when M21GB is used as the reference preparation and for iodination. Finally, antisera to M21GB were generated in rabbits which are specific for monkey and human prolactin and which can be used for radioimmunoassay or immunocytochemistry. In summary, serum-free medium from primary cultures of dispersed monkey pituitaries provided a quantitity of monkey prolactin which promoted biochemical analysis and production of a specific antiserum. This culture system may be a unique and ongoing source for extraction of significant quantities of monkey prolactin suitable for investigative use.

Amino Acids↗

PubMed1985

Isolation and properties of sea turtle (Chelonia mydas) pituitary prolactin.

Sea turtle prolactin (PRL) was isolated in a highly purified state from sea turtle pituitary side fractions obtained from other studies and some of its biological, chemical, and immunological properties were determined. Sea turtle PRL is a protein of 22-24 kDa [sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis]. Its sole amino terminal amino acid residue is leucine. The amino acid composition of sea turtle PRL is similar to ovine PRL and is characterized by a high content of aspartic acid (20 residues), glutamic acid (34 residues), serine (19 residues), and leucine (24 residues). It possess three disulfide bonds and 2 tryptophan residues which is also characteristic of many species of PRL. As with PRLs of other species, it displayed multiple stained bands in disc gel electrophoresis, at pH 8.3. Biologically, sea turtle PRL was active in pigeon crop-sac assay but the dose-response characteristics were nonparallel when compared to ovine PRL. An antiserum against sea turtle PRL was raised in rabbit and a homologous radioimmunoassay was developed with a sensitivity of 2.8 ng for sea turtle PRL. Sea turtle gonadotropins did not cross-react, but sea turtle growth hormone showed a 5% cross-reactivity. Pituitary extracts from other species of turtles displayed parallel inhibition curves to the sea turtle PRL. Extracts and prolactin preparations from several birds, snakes, alligator, and marsupials cross-reacted, but in a nonparallel fashion. Bullfrog pituitary extract and Tilapia PRL showed no cross-reaction at high doses. Several purified mammalian PRLs (pig, sheep, human, horse, dog) showed minimal or no ability to cross-react in the RIA.

Amino Acids↗

PubMed1985

Reevaluation of the relative activities of the pituitary glycoprotein hormones (follicle-stimulating hormone, luteinizing hormone, and thyrotrophin) from the green sea turtle, Chelonia mydas.

The discovery that the follicle-stimulating hormone (FSH) previously prepared from the green sea turtle, Chelonia mydas, contained a major neurohypophysial contaminant prompted a repurification and characterization of the glycoprotein hormones in this turtle. Results reaffirmed the physicochemical distinctiveness of the three hormones. Minimal cross-contamination between hormones (less than 2%) was achieved by ion-exchange chromatography, subunit dissociation (of contaminating luteinizing hormone (LH], gel filtration, and immuno-affinity chromatography. New preparations of FSH and thyrotrophin (TSH) derived from adult pituitaries proved to be more potent than those described previously (the degree depending on the nature of the assay); FSH showed the expected increase in activity based on estimated contamination of previous preparations. LH was similar to original preparations except for enhanced activity in FSH radioreceptor assays. Binding assays (in heterologous and homologous systems) again demonstrated the general absence of an FSH-specific receptor in the reptilian (chelonian and squamate) testes. In an in vivo bioassay in the lizard Anolis, the turtle FSH was orders of magnitude more potent than LH in stimulating both testis growth and androgen secretion, but in vitro LH was considerably more potent than FSH in stimulating androgen secretion in squamate and chelonian testes. Thus, the possibility exists that androgen secretion in some chelonian systems may exhibit a high degree of LH specificity like that of mammals and birds.

Androgens↗

PubMed1985

Ovulations in rat ovaries perfused in vitro with follicle-stimulating hormone.

Using the model of the isolated perfused rat ovary, we have found that highly purified ovine follicle-stimulating hormone (FSH) preparations cause ovulation and that this effect is not due to luteinizing hormone (LH) contamination. Ovine FSH-13 at a concentration of 1.5 mU/ml induced ovulations in all perfused ovaries (8.8 +/- 2.3 ovulations/ovary), as did a more purified preparation, ovine FSH-211B, at concentrations of 0.5 mU/ml (15.0 +/- 6.4 ovulations/ovary) and 5 mU/ml (11.3 +/- 2.6 ovulations/ovary). This ovulation-inducing effect of FSH is accompanied by a marked stimulation of estradiol levels in the perfusion medium without stimulation of progesterone levels. Furthermore, a purified rat FSH preparation (15 mU/ml) also induced ovulation in all ovaries (13.8 +/- 2.2 ovulations/ovary) as well as a stimulation of both estradiol and progesterone in the medium. These data clearly confirm the direct ovulatory effect of FSH on the ovary.

Animals↗

PubMed1985

Nonmammalian growth hormones have diabetogenic and insulin-like activities.

Purified GHs isolated from ostrich, sea turtle, snapping turtle, bullfrog, Tilapia, and sturgeon were tested for in vivo diabetogenic activity in the hereditarily obese ob/ob mouse and for in vitro insulin-like activity in isolated adipose tissue from hypophysectomized rats. GHs from all species exhibited significant diabetogenic activity, causing fasting hyperglycemia and decreased glucose tolerance when administered at doses of 100 micrograms/day (ostrich, bullfrog, and sturgeon) or 200 micrograms/day (sea turtle, snapping turtle, and Tilapia) for 3 days. Similar responses were obtained when purified human GH was administered at a dose of 10 micrograms/day for 3 days. GHs from most species also exhibited significant insulin-like activity, stimulating increased [14 C]glucose oxidation to 14CO2 by isolated adipose tissue from hypophysectomized rats when employed at concentrations of 50 nM (bullfrog), 250 nM (sturgeon), 500 nM (ostrich), or 2500 nM (sea turtle and Tilapia). Purified human GH gave similar responses at concentrations of 2.5-5 nM in this assay. These results support the hypothesis that diabetogenic and insulin-like activities are intrinsic properties of GH and provide strong evidence that the structural determinants for diabetogenic and insulin-like activities arose early in the evolution of the GH molecule.

Animals↗

PubMed1984

Chemical, biological and immunological properties of pituitary gonadotropins from the donkey (Equus asinus): comparison with the horse (Equus caballus).

Donkey gonadotropins (donkey luteinizing hormone, dLH; donkey follicle-stimulating hormone, dFSH) have been isolated in purified form from 191 donkey pituitaries using essentially the same procedures previously employed for the purification of equine gonadotropins. Chemically, dLH and dFSH were observed to be similar to equine LH (eLH) and FSH (eFSH) in fractionation behavior and glycoprotein nature. Two forms of the dFSH molecule were observed, as is the case for eFSH. Donkey LH had significantly less total carbohydrate (13.5%) and sialic acid (1.9%) than eLH (26.7% and 5.8%, respectively). Carbohydrate (17-21%) and sialic acid (2.4%) content of the two dFSH preparations closely resembled that of eFSH. A slightly higher tyrosine content in the donkey gonadotropins was noted in a comparison of amino acid compositions. Immunologically, in a heterologous FSH radioimmunoassay (RIA), dFSH preparations were equal to or twice as active as eFSH preparations. However, in homologous RIAs for equine chorionic gonadotropin (eCG), eFSH and eLH, both the dLH and dFSH preparations were considerably less active than the equine gonadotropins, and their inhibition curves were all nonparallel. Biologically, in the Steelman-Pohley assay both dFSH preparations were equipotent and as potent as eFSH (approximately 40 times NIH-FSH-S12). In the Sertoli cell assay for cAMP (FSH assay) and the Leydig cell assay for testosterone (LH assay), both dFSH and dLH were 2- or 6-fold more active than eFSH and eLH, respectively. In rat and equine testis FSH homologous radioreceptor assays, dFSH preparations were as active and up to 6-fold more active than eFSH. In contrast, dLH was 10-fold less active than eLH in the equine LH homologous radioreceptor assay. Unlike eLH, dLH was found to possess little intrinsic FSH activity or FSH inhibitory activity, and the small amount of FSH activity observed was most likely due to FSH contamination. Therefore, eLH behaves much like eCG (pregnant mare's serum gonadotropin, PMSG) which also possesses both LH and FSH activity. In contrast, dLH behaves more like donkey chorionic gonadotropin (dCG) which possesses only a low degree of FSH activity.

Animals↗

PubMed1984

Hourly administration of luteinizing hormone induces ovulation in prepubertal female sheep.

This investigation examined the effects of repeated injections of LH on ovarian function in the immature sheep approximately 12 weeks before the time of the first expected spontaneous ovulation. The frequency of endogenous LH pulses during the pretreatment period was approximately one pulse each 3 h. The first experiment determined that rapid injection (iv) of 15.5 micrograms LH replicated the amplitude of endogenous pulses. Hourly injection of this dose for 48 h to simulate the rapid LH pulse frequency of the follicular phase of the postpubertal female induced a LH surge and ovulation in two of three lambs. By contrast, administration of 33% of the dose over the 48-h period did not [5.2 micrograms/h (three lambs) or 15.5 micrograms each 3 h (three lambs)]. The second experiment (seven lambs) determined the time course of the preovulatory estradiol rise produced in response to hourly LH pulses (15.5 micrograms/injection), as well as the length of the luteal phase after the induced LH surge. Four lambs produced a sustained estradiol rise, a LH surge, and ovulation. The luteal phase was normal (13 days) in one and short in three lambs (6-11 days). In the remaining three prepubertal females that did not ovulate in response to 48-h injections of LH, the estradiol rise was not sustained. Circulating estradiol in five untreated control lambs exhibited only transient increases during the course of the study. The results indicate that hourly administration of physiological quantities of LH over a relatively brief period (48 h) can produce a follicular phase culminating in first ovulation in the immature lamb. In the context of the mechanism proposed for puberty in the female sheep, the findings are consonant with the hypothesis that the hypothalamus, through its modulation of LH pulse frequency, governs the initiation of ovulation.

Animals↗