Involvement of the calcium-specific protease, calpain, in the fertilizing capacity of human spermatozoa

We recently reported the novel finding that human spermatozoa contain the calcium (Ca2+)-dependent protease, calpain. In somatic cells this protease mediates several cellular activities regulated by Ca2+ including membrane fusibility during cell-to-cell interactions. In this paper we examined the participation of sperm calpain in sperm-oocyte penetration, a process that is dependent on Ca2+ and involves membrane fusion between the two cells. Oocyte penetration was assessed using ejaculated spermatozoa from fertile men and zona-free hamster oocytes. Penetration rate was impaired by the presence of the active-site calpain inhibitor, calpain inhibitor-I, in a dose-dependent manner. At 1 mM, penetration scores were reduced by 65% (p < 0.01; n=5). The effects did not involve the oocyte, nor did the inhibitor alter sperm motility. Similar inhibitory effects on sperm penetration capacity were observed with specific antibodies directed either against calpain-I or calpain-II, the two forms of calpains described in somatic cells. At 1:1000 antibody dilution, penetration was inhibited 50 and 60% with anti-calpain-I and anti-calpain-II antibodies, respectively (p < 0.01; n=6). Furthermore, a combination of these two antibodies reduced the penetration rates by 75% (p < 0.01; n=6). We conclude that calpain inhibitor and anti-calpain antibodies impair human sperm capacity to fuse and penetrate the oocyte. These findings suggest that sperm calpain is a novel component of the biochemical processes that regulate the fertilizing capacity of human spermatozoa.

Changes in expression of adenyl cyclase activity in human endometrium during hormone replacement therapy and ovarian stimulation

We have investigated membrane fractions prepared from human endometrium for activity of the signalling adenyl cyclase (AC). We characterized the AC guanine nucleotide-binding proteins (G proteins) and examined the changes in AC activity during evaluation cycles of oestrogen and progesterone replacement therapy as well during ovarian stimulation cycles. AC activity was determined by the conversion of substrate ATP into cyclic AMP under basal conditions and in the presence of guanine nucleotide or forskolin. G proteins were determined by Western Blot using specific polyclonal antibodies against Gsalpha, Gi1,2alpha and Gi3alpha. Our results indicate that endometrial AC was highly responsive to activation by both guanine nucleotide and forskolin and its rate of cyclic AMP production was highly pronounced. Mean activity reached 920 pmol/l/min/mg membrane protein in the presence of forskolin, a value approximately 5-fold higher than those detected in corpus luteum. Hormonal induction of AC activities increased Gsalpha protein, which couples with and stimulates the catalytic component of AC. We conclude that human endometrium is rich in AC and that enzyme activity is induced by oestrogen and progesterone treatment. These data strongly support the concept that the transmembrane signalling AC system and its messenger cyclic AMP are major regulators of endometrial function in the human.

Calpain-calpastatin: a novel, complete calcium-dependent protease system in human spermatozoa

Calpain, a calcium (Ca2+)-activated cysteine protease presents in several somatic mammalian cells, has been demonstrated to mediate specific Ca2+-dependent reactions including cell fusion. Because spermatozoa cells have an absolute Ca2+ requirement for penetration of oocytes, we have postulated that calpain would also be found in mammalian spermatozoa. Here we show that whole sperm homogenate and cell fractions prepared from ejaculated human spermatozoa contain calpain activity. Specific calpain inhibitors impaired this proteolytic activity. Unlike the enzyme described in somatic cells, sperm calpain was mostly particulate in nature and its activity was maximal at pH 9.0. Presence of sperm calpain was confirmed by immunoblot analysis using specific anti-calpain I and anti-calpain II antibodies. A 67 kDa calpain II protein and a 75 kDa calpain I protein were detected. Also spermatozoa contain the endogenous calpain inhibitor, calpastatin. We detected 158.8 +/- 24.5 (mean +/- SD) fmol calpastatin/mg sperm protein. Immunoblot analysis using specific antibodies showed a 68 kDa calpastatin protein located in the cytosolic fraction. This is the first demonstration that a complete calpain-calpastatin system exists in mammalian spermatozoa. Because calpain is a unique effector system for calcium-dependent processes, our data reveals a novel mechanism by which calcium exerts its regulatory functions in spermatozoa.

Enzymatic amplification of specific deoxyribonucleic acid sequences from single cells: evaluation of a simplified and rapid method for use in preimplantation genetic diagnosis

OBJECTIVE

To develop a simplified polymerase chain reaction (PCR) protocol on single cells for the purpose of preimplantation genetic diagnosis. Also to evaluate a new thermal cycler, RoboCycler 40 (Stratagene, La Jolla, CA), for reducing the time to complete PCR amplification.

DESIGN

PCR amplification without DNA purification or reamplification of a 149 base pair (bp) segment of the human Y chromosome was used as a model. The assay was tested in human fetal cells, single lymphocytes and single human blastomeres.

RESULTS

Amplification of the 149 bp segment using fetal cells was 100% correct. Results on single lymphocytes were concordant in all but one of the 15 male cases. However, 2 of the 25 female cases were identified as male suggesting the occurrence of DNA contamination. Analysis of 61 blastomeres were concordant in 57 cases (93%); results for male blastomeres showed 12% of false negatives. No false positives were detected for female cells. Amplification using the simplified PCR protocol in combination with the RoboCycler was completed in 2 hours.

CONCLUSION

These data show that this PCR assay performed directly, without DNA extraction or purification and without re-amplification is a practical and effective approach for amplification of specific DNA sequences in single cells. Furthermore, the simplified PCR protocol significantly reduced the time to complete DNA amplification. The reduced time is expected to facilitate the management of a routine program for preimplantation genetic diagnosis.

Status of hCG/LH receptor and G proteins in human endometrium during artificial cycles of hormone replacement therapy

OBJECTIVES

We examined the existence of hCG/LH receptors and associated GTP-binding (G) proteins in membrane fractions of nonpregnant human endometrium and investigated whether their expression is affected, in vivo, by estrogen and progesterone replacement therapy.

METHODS

A pool of normal endometrial biopsy specimens (n = 5) was initially used to characterize receptors and G proteins. Subsequently, biopsy specimens (n = 22) were obtained from 11 patients undergoing evaluation cycles of hormone replacement therapy (HRT). From each patient, two specimens were collected on successive cycle days: on day 0 (last day of estrogen) and on either day 3, 6, or 9 of progesterone supplementation. Both hCG/LH receptor and G proteins were determined in membrane (10,000 x g) fractions by immunoblot analysis using specific polyclonal antibodies against synthetic fragments of hCG/LH receptor and against G proteins. Membrane fractions from rat brain and rat corpus luteum were used as controls. Proteins were loaded on the gel under reducing conditions.

RESULTS

The receptor antibody immunoreacted with a protein of approximately 68 kd in endometrial membranes. A similar protein was detected in rat corpus luteum. The G-protein antibodies detected Gs alpha, Gi3 alpha, Gi1 alpha/Gi2 alpha, and common beta subunits in endometrial membranes with a molecular weight of 48-42 kd, 41 kd, 40 kd, and 37 kd, respectively. Analysis of membranes obtained during HRT indicated that levels of hCG/LH receptors remained fairly constant throughout the cycle days (days 0, 3, 6, and 9). Similar results were observed for Gi1 alpha/Gi2 alpha and Gi3 alpha. In great contrast, Gs alpha was low at day 0 but increased with the administration of progesterone (days 3, 6, and 9).

CONCLUSIONS

Human endometrium contains both membrane-bound hCG/LH receptors and associated G proteins. During HRT, progesterone supplementation to estrogen therapy enhances the expression of Gs alpha protein subunit, but not hCG/LH receptors.

Evidence for a novel adenylyl cyclase in human epididymal sperm

Since cAMP is considered to play a major role in the acquisition of maturation and fertilizing capacity of mammalian sperm, we investigated the expression of cAMP-synthesizing adenylyl cyclase (AC) in sperm retrieved directly from the human epididymis. Particulate fractions were prepared from purified epididymal sperm samples and AC was monitored by the direct conversion of ATP into cAMP. We report that in great contrast to human ejaculated sperm and other mammalian sperm cells, the human epididymal sperm do not express a Mn(2+)-sensitive AC. However, a functional AC was readily detectable in these sperm cells in the presence of saturating concentrations of Ca2+ (50mM) and bicarbonate (HCO3-, 50mM), a combination that causes maximal activation in human ejaculated sperm. Using these conditions, human epididymal sperm AC showed similar capacity to generate cAMP compared to human ejaculated sperm AC. When assays were performed in the presence of Mg2+ and a saturating concentration of GMP-P(NH)P (50 microM), the hydrolysis-resistant GTP analog, and forskolin (100 microM), no activity was detected indicating that the epididymal sperm AC differs from that in somatic cells. These data demonstrate that human epididymal sperm contain an AC that is unique and different from the enzyme system described in somatic cells and other mammalian sperm cells, including human ejaculated sperm.

Relationship of epididymal sperm antibodies to their in vitro fertilization capacity in men with congenital absence of the vas deferens

OBJECTIVES

To test, using the immunobead binding technique, for the presence of antisperm antibodies on epididymal sperm, in epididymal fluid, and in serum of men with congenital absence of the vas deferens. To evaluate the in vitro fertilization (IVF) capacity of human epididymal sperm in the presence of antisperm antibodies.

DESIGN

Prospective. At the time of oocyte insemination, sperm from the proximal caput epididymis or vasa efferentia were tested by direct immunobinding technique. The epididymal fluid and serum were tested by indirect immunobinding technique.

SETTING

Center for Reproductive Health, University of California-Irvine.

PATIENTS

Forty-five patients with congenital absence of the vas deferens participating in the microsurgical epididymal sperm aspiration and IVF program.

MAIN OUTCOME MEASURE

Incidence of antisperm antibodies to epididymal sperm and their relationship with IVF results.

RESULTS

Sixteen men (35%) tested positively to the direct immunobead test on epididymal sperm; 7 (16%) were positive in epididymal fluid and 13 (29%) were positive in serum. Five pregnancies (31%) occurred in the positive group of which two were from patients who had sperm binding of 100% for immunoglobulin (Ig)G (all over sperm surface) and 90% (midpiece, tail) and 50% (tail, tiptail), respectively, for IgA. Five pregnancies (18%) were obtained in the negative group. No statistical difference was observed in the overall fertilization rate between the two groups.

CONCLUSION

Human epididymal sperm and epididymal fluid retrieved from men with congenital absence of the vas deferens can react positively to immunobead test. However, the presence of antisperm antibodies do not seem to impair the IVF capacity of epididymal sperm.

Regulation of cyclic adenosine monophosphate synthesis in human ejaculated spermatozoa. II. The role of calcium and bicarbonate ions on the activation of adenylyl cyclase

In this study, we have applied our previous data describing the experimental conditions necessary for expression of cyclic adenosine monophosphate (cAMP)-synthesizing adenylyl cyclase in human ejaculated spermatozoa, to investigate the direct effects of calcium (Ca2+) and bicarbonate (HCO3-) upon activation of the enzyme in vitro. We report that the effects of Ca2+ and HCO3- were significantly dependent on the status of the enzyme activity. Thus, at a near saturating (10 mM) concentration of MnCl2 giving high enzyme activity, addition of less than 10 mM HCO3- did not affect adenylyl cyclase activity and higher concentrations inhibited the enzyme, with 50 mM HCO3- reducing the activity by 33%. Also, addition of less than 20 mM CaCl2 alone or in combination with 10 mM HCO3- did not significantly change the enzyme activity. In great contrast, enzyme activation was highly responsive to Ca2+ and HCO3- when MnCl2 was present at a concentration giving submaximal enzyme activity. Thus, at 2 mM MnCl2, adenylyl cyclase was markedly increased by CaCl2 concentrations between 10 and 100 mM. The activation was further enhanced by increasing concentrations of HCO3-, with 50 mM HCO3- giving the highest activity at 50-100 mM CaCl2. Activation by CaCl2 was also observed in the absence of added MnCl2, being significantly greater than basal activity at 10 mM CaCl2 and maximal at 100 mM CaCl2.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of the adenylyl cyclase system in the regulation of corpus luteum function in the human and in nonhuman primates

We have reviewed the properties of luteinizing hormone/human chorionic gonadotropic (LH/hCG)-sensitive adenylyl cyclase (AC) of human corpus luteum (CL) and its regulation by several hormones and nonhormonal activators. We have also described the changes in enzyme activity in membrane preparations of human and cynomolgus monkey CL obtained at various stages of the menstrual cycle and pregnancy. The data have been analyzed with respect to the functional status of the luteal tissue and to the species differences among primate CL. In the menstrual cycle, luteal AC responsiveness to LH/hCG was detectable during the midluteal phase, but not during the late luteal phase or in the follicular phase of the following cycle. In addition, nonhormonal stimulation was high in CL obtained during the midluteal and late luteal phases, but declined drastically by the follicular phase of the next cycle. In early pregnancy, the enzyme was unresponsive to LH/hCG stimulation, yet its sensitivity to nonhormonal stimulation was similar, if not identical, to that of midluteal phase CL. Functional activity was also evident at the end of pregnancy. These results demonstrate that expression of AC activity in primate luteal membrane changes significantly with varying hormonal status under physiologic conditions. It is concluded that the AC system in luteal membranes is an effective model to study the mechanisms that regulate function and life span of the human and nonhuman primate CL.

Insulin-like growth factors and thecal-granulosa-cell function

Insulin-like growth factors (IGFs) belong to a family of low mol. wt, single chain polypeptides inducing growth promotion and insulin-like metabolism effects and regulating both cell replication and differentiation. Recent studies in laboratory animals suggest that IGFs play an important role as intraovarian regulators in several mammalian species. The purpose of this article was to review current concepts of interactions between the IGFs and the thecal-granulosa-cell function. To provide a basic understanding of these interactions, we have first analysed data concerning biosynthesis, biochemical structure, pharmacokinetics, degradation, binding proteins and receptors for IGFs. Then we have discussed the specific interactions between IGFs and theca-granulosa-cell regulation, and analysed the significance of the relationship to the pathophysiology of some endocrine and reproductive disorders, including hyperandrogenism and female infertility.

Intrauterine inseminations with washed human spermatozoa does not induce formation of antisperm antibodies

In this study we investigated the possible development of serum antisperm antibodies in women receiving repeated IUI. Patients acted as its own control and were evaluated before and after various (1 to 15) IUI cycles using three different assays for antisperm antibodies. It was found that only 2 out of 41 women developed antisperm antibodies. We concluded that exposure of the upper reproductive tract to washed spermatozoa during repeated IUI with partners' sperm does not significantly stimulate the appearance of serum antisperm antibodies.

Low incidence of sperm antibodies in men with congenital absence of the vas deferens

The incidence of antisperm antibodies in serum and seminal fluid of 27 azoospermic men with congenital absence of the vas deferens is evaluated. The presence of antisperm antibodies was assessed using the immunobead test, the agglutination test, and immobilization test. Five patients with vasovasostomy or vasoepididymostomy attempts were included in the study and tested for the presence of antisperm antibodies. Contrary to a previous report, a low incidence (11%) of antisperm antibodies has been found in patients with congenital absence of the vas. In agreement with previous studies, in five patients who had failed vasoepididymostomy or vasovasostomy, a high incidence (71%) of antisperm antibodies was found.

Expression of insulin-like growth factor-II (IGF-II) messenger ribonucleic acid (mRNA), but not IGF-I mRNA, in human preovulatory granulosa cells

Increasing evidence suggests that insulin-like growth factors (IGFs) play an important role as intra-ovarian regulators in several mammalian species. Recently, we and others have reported the presence of both IGF-I and IGF-II in human follicular fluid. The source of these follicular IGFs, however, has not been determined. In this study, we have evaluated the possibility that human ovarian granulosa cells are a production site of IGFs in vivo. We used cDNA probes to analyse directly IGF-I and IGF-II gene expression at the level of mRNA content in granulosa cells from preovulatory follicles of women undergoing either gamete intra-Fallopian transfer or in-vitro fertilization. Samples of granulosa cell RNA enriched for polyadenylated RNA [poly(A)+RNA] were hybridized with probes for human IGF-I, human IGF-II and human actin (as a control). Transfer blot analysis revealed that the enriched poly(A)+RNA of human granulosa cells from preovulatory follicles contained no detectable IGF-I mRNA. In contrast, three species of IGF-II mRNA of approximately 6.1, 4.9 and 2.1 kb were detected. These data suggest that IGF-II mRNA, but not IGF-I mRNA, is expressed in human granulosa cells collected immediately before ovulation. Our results support the concept that human ovarian IGF-II is produced locally and may function in an autocrine or paracrine fashion in the human ovary in vivo.

Delayed occurrence of an LH surge after HCG administration during ovarian stimulation with gonadotrophins: effect of LHRH treatment

Previous studies have shown the appearance of a spontaneous luteinizing hormone (LH) surge after human chorionic gonadotrophin (HCG) administration in human menopausal gonadotrophin (HMG)/HCG-stimulated menstrual cycles. In this report we investigated the effect of leuprolide acetate, a long-acting luteinizing hormone releasing hormone (LHRH) agonist, on the occurrence of these post-HCG rises in serum LH. Two groups of patients were included. Group 1: 10 patients receiving HCG as a part of an HMG/HCG protocol for induction of follicular development in an IVF/GIFT program and Group II: 10 patients treated as Group I, but receiving the LHRH agonist leuprolide acetate to inhibit gonadotrophin secretion prior to and during ovarian stimulation. In Group I, none of the patients showed a surge prior to HCG administration. However, an LH surge following HCG treatment was apparent in four patients (40%). Pregnant patients (2/10) had low mean levels (less than or equal to 2.5 mIU/ml LH) in the follicular phase and showed no LH surge after HCG. In Group II, baseline levels of serum LH were reduced significantly (mean, 1.4 +/- 0.1 mIU/ml; P less than 0.001) compared to Group I. No patient showed an LH surge either before or after HCG administration and the occurrence of pregnancy was higher (6/9 transfers) than in Group I. In spite of the differences in pregnancy rates, the combined therapy versus HMG therapy showed no significant difference in number of oocytes collected or serum oestradiol levels. This suggests that high levels of serum LH, whether prior to or after HCG administration, may have a detrimental effect on the establishment of pregnancy despite adequate follicular growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility of the indirect immunobead assay for detecting sperm antibodies in serum

Although an immunobead assay (IBA) for the detection of antisperm antibodies was developed several years ago and has been used for the study of immunologic infertility, no data regarding its variability and reproducibility are yet available. We evaluated the intraassay reproducibility of the indirect IBA by testing aliquots of antisperm-antibody-positive sera from two patients against the same donor sperm sample. The interassay reproducibility was evaluated by testing a positive serum sample first with different sperm samples from the same donor and second with sperm samples from different donors. The results of those experiments showed that the indirect IBA has very low intraassay variation and greater interassay variability.

Regulation of gonadotropin-stimulable adenylyl cyclase of the primate corpus luteum

In an effort to understand the molecular mechanisms that control luteal function in the human and nonhuman primates, we have investigated the experimental conditions for expression of gonadotropin-induced adenylyl cyclase (AC) in membrane particles from primate corpus luteum (CL) and some of the factors modulating the enzyme activity. We also examined the usefulness of the cell-free model for studying the role of AC in the regulation of CL functions in human and nonhuman primates. Enzyme activity was dependent on guanine nucleotide and Mg ion. Dose-response curves showed that the AC activation constants for hCG was about 0.1 microgram/ml. This value did not shift after the addition of guanine nucleotide. Enzyme responsiveness to prostaglandin E2 was small and, in contrast to a number of other nonprimate species, AC from the human CL was not stimulated by catecholamines. Calcium directly inhibited responsiveness of hCG-sensitive AC; inhibition was significant at 0.5 mM CaCl2 (in the presence of 1 mM EDTA and 2 mM ATP), being 90% at 2.5 mM CaCl2. These results support the concept that Ca2+ might play a role in the regulation of gonadotropin action and life span of human CL. Changes in AC activities during luteal phase and pregnancy were similar in the CL of monkeys and humans. Thus, in both cases, maximal gonadotropin responsiveness was observed during the midluteal phase. Also, during pregnancy (term and early pregnancies), responsiveness to exogenous hCG in vitro was very low, but the enzyme was readily responsive to NaF (10 mM) and forskolin (100 microM). These activities suggest that the tissue remains functionally active during pregnancy. It is concluded that the cell-free AC system is an effective model to study the cellular mechanisms that regulate luteal function in human and nonhuman primates.

A cDNA for the estradiol-regulated 24K protein: control of mRNA levels in MCF-7 cells

We have previously demonstrated an estradiol-regulated 24 kDa (24K) protein in human breast cancer tissue culture cells and human tumor biopsies. The presence of 24K correlates well with the presence of steroid hormone receptors. In order to further study the hormonal regulation of the 24K protein and gene, we have isolated cDNA clones corresponding to the 24K mRNA. Poly(A)+ RNA isolated from the MCF-7 human breast cancer cell line was translated in a cell-free translation system containing [35S]-methionine. The translation products were immunoprecipitated with a 24K monoclonal antibody, and the in vitro synthesis of 24K protein was confirmed by sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis. The same poly(A)+ RNA was used to construct an oligo(dT)-primed cDNA library in the lambda gt11 expression vector system. The library was screened with a highly specific polyclonal antibody raised against 24K protein purified by immunoaffinity chromatography. Four recombinant clones reacting with the antibody by virtue of antigen expression were isolated and three were used in hybridization-selected translation. Three clones were able to hybridize specifically to a messenger RNA (mRNA) that yielded a Mr 24,000 protein when translated in vitro and analyzed by SDS/polyacrylamide gel electrophoresis. This protein was also immunoprecipitable by the 24K monoclonal antibody. MCF-7 mRNA size fractionated by formaldehyde-agarose gel electrophoresis was transferred to nitrocellulose paper and hybridized to a nick-translated 24K cDNA clone. A single band of hybridization corresponding to a mRNA size of approximately 0.9-1.0 kilobase (kb) was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of serum luteinizing hormone during ovarian stimulation with gonadotrophins

An immunoradiometric assay (IRMA), using monoclonal antibodies with high affinity for human luteinizing hormone (HLH), was evaluated for quantitative measurement of serum LH after human chorionic gonadotrophin (HCG) administration in patients undergoing stimulation of multiple follicular development. Compared to a radioimmunoassay (RIA) commonly used to monitor serum LH, LH IRMA was more effective by several orders of magnitude in discriminating between HLH and HCG and showed no cross-reactivity at HCG concentrations normally found in serum after hormone treatment. Assays of serum samples obtained from 10 patients receiving HCG as part of an HMG/HCG protocol to induce ovulation for IVF/GIFT also demonstrated that RIA values were greatly affected by exogenous HCG. It was estimated that 17-32% of serum HCG was measured as serum LH in RIA. In contrast, determinations of serum LH by IRMA was not biased by exogenous HCG. Data from IRMA indicated that eight of the 10 patients showed a significant rise in LH secretion, relative to mean baselines, at either 12 or 36 h after administration. In one patient the rise had already occurred before HCG administration. When an LH rise occurred, either before or after HCG injection, mean values were 2- to 9-fold higher than those of baseline levels. Assuming that LH rises greater than 12 mIU/ml may relate to an endogenous surge of LH, none of the patients showed a surge prior to HCG administration. On the contrary, the occurrence of an 'LH surge' after HCG was apparent in four patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotonergic and adrenergic regulation of skeletal muscle metabolism in the rat. II. The use of [125I]iodolysergic acid diethylamide and [125I]iodopindolol as probes of sarcolemmal receptor function and specificity

To evaluate serotonin receptor kinetics in skeletal muscle, we synthesized and developed 2-[125I]iodolysergic acid diethylamide [( 125I]iodoLSD) as a high affinity, high specific activity probe of serotonergic receptor function. The kinetics of binding of this probe and the profile of agonist and antagonist displacement have been compared to results obtained using [125I] iodopindolol as a probe for beta-adrenergic receptor binding. [125I]IodoLSD was prepared by chloramine-T iodination and purified by high pressure liquid chromatography. Fluorescence, ultraviolet, and nuclear magnetic resonance spectra as well as mass spectroscopy demonstrate that the iodinated compound is 2-iodoLSD. This probe bound in a concentration-dependent fashion to sarcolemma in a manner consistent with existence of a single population of specific receptors having a Kd of 1.46 nM and an abundancy of 47 fmol/mg of protein. Half-maximal binding of the probe occurred within 1.0 min and equilibrium binding was observed at 8.0 min. The apparent t 1/2 for the probe-receptor complex was 40 s; the Kd calculated from kinetic data was 1.69 nM. The IC50 for displacement of iodoLSD was 330 +/- 185 nM for methysergide, 757 +/- 309 nM for cyproheptadine, and 2,570 +/- 1,390 nM for serotonin. Adrenergic antagonists such as l-propranolol and oxprenolol also displaced [125I]iodoLSD, but did so with IC50 values of 17,800 +/- 5,100 and 23,300 +/- 5,500 nM, respectively. Using [125I]iodopindolol as a receptor probe, we found the order of potency for adrenergic antagonists to be l-propranolol greater than oxprenolol much much greater than practolol. Serotonergic antagonists, although effective in displacing [125I]iodopindolol, did so only at very high concentrations. These results are consistent with the existence of separate and discrete D-serotonergic and beta 2-adrenergic receptors in skeletal muscle and the finding that adrenergic agonists and antagonists may interact with low affinities with the serotonergic receptor, but that serotonergic agonists and antagonists interact poorly, if at all, with the beta 2-adrenergic receptor.

Effects of tristearin, triolein and safflower oil diets on cholesterol balance in rats

Diets containing relatively homogeneous triglycerides composed of 18-carbon chain saturated, monounsaturated or polyunsaturated fatty acids were fed to rats. Cholesterol absorption and turnover were studied. Cholesterol absorption was significantly less in rats fed tristearin than in animals fed triolein or safflower oil. Cholesterol removal from plasma was fastest in rats fed tristearin and slowest with safflower oil and triolein. Plasma cholesterol levels were lowest with tristearin and highest with safflower oil. Increased cholesterol in high density lipoproteins was observed with tristearin and triolein. Lymph and hepatic cholesterol, and lymph triglycerides were highest with safflower oil, suggesting endogenous mobilization. Cholesterol production was least with triolein. Sterol synthesis was greatest with tristearin, perhaps attributable to decreased negative feedback analogous to effects of cholestyramine. Differences in lipoprotein composition observed with the various diets are important since effects on particle size and shape may influence removal mechanisms. The mechanisms underlying the different effects of dietary triglycerides on sterol absorption and metabolism remain to be elucidated.

Effects of diets of homogeneous saturated triglycerides on cholesterol balance in rats

The effects of a diet of 10% homogeneous triglycerides of 12 to 18-carbon chain saturated fatty acids on cholesterol absorption and turnover were studied in rats. Cholesterol absorption was successively significantly less in rats fed tristearin than in groups fed tripalmitin, trimyristin and trilaurin. Lesser fatty acid absorption may explain the differences in part, since cholesterol absorption was significantly correlated with fat absorption. Cholesterol removal from plasma was fastest in rats fed tristearin. Plasma cholesterol levels were increased with the trilaurin diet although the rate of cholesterol accumulation in lymph after gavage was slower with trilaurin. Lymph triglycerides were highest with trilaurin and trimyristin diets perhaps indicating endogenous mobilization of triglyceride for lipoprotein formation. Lymph triglycerides were, however, decreased with tristearin. Sterol turnover (production, absorption plus synthesis) was increased with tristearin or trilaurin by kinetic or balance methods.