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Biomedical subjects

I T Huhtaniemi

Publications and source records attributed to I T Huhtaniemi.

At least 19 recordsLinked to original sources
PubMed1995

Functional maturation of the pituitary-gonadal axis in the neonatal female rat.

The development onset of the pituitary feedback response to LH/hCG-stimulated ovarian activity was studied in the neonatal rat. A single injection of hCG (600 IU/kg BW) was administered to groups of rats between 1 and 10 days of age, and the responses, i.e., ovarian estradiol (E2), progesterone (P), and testosterone (T) production as well as serum LH were monitored 3 days later. The first significant increase in ovarian T and E2 contents occurred in rats treated on Day 8 of life, and the first significant increase in P content occurred when hCG was administered at the age of 9 days. A significant decrease in serum LH, 3 days after hCG injection, was observed for the first time in animals treated on Day 7, but not in those aged 1-6 days. To study whether the appearance of the ovarian response to LH is dependent on FSH, rats received combined treatment with recombinant human (rec)FSH on Days 3-8 (0.3 IU s.c. twice daily) and a single injection of hCG (600 IU/kg BW s.c.) on Day 6. The elevated FSH levels from Day 3 onward advanced the suppression of the serum LH level after hCG injection, suggesting that enhanced action of FSH promotes the appearance of functional LH receptors neonatally. It was concluded that 1) the negative feedback of ovarian activity on pituitary LH secretion is functional in the neonatal rat from Day 10 of life; 2) increased intraovarian T levels reflect the androgenic dominance of this early feedback action; and 3) elevated postnatal levels of FSH may advance the onset of the ovarian response to LH/hCG stimulation.

Aging↗
PubMed1995

Gonadal tumorigenesis in transgenic mice bearing the mouse inhibin alpha-subunit promoter/simian virus T-antigen fusion gene: characterization of ovarian tumors and establishment of gonadotropin-responsive granulosa cell lines.

To establish in vivo gonadal tumor models and permanent lines of gonadal somatic cells we produced transgenic (TG) mice expressing the Simian virus (SV) 40 T-antigens (T-ag), driven by 6 or 2.1 kilobase fragments of the mouse inhibin alpha-subunit promoter. Hitherto, altogether 44 TG mice, one of which carried the shorter transgene, have produced gonadal tumors. Two founder females expressing the longer transgene, KK1 and KK3, and three established TG mouse lines were studied in detail. Penetrance of the phenotype in IT6-M and IT6-F mouse lines was 100% (tumors/TG: IT6-M 22/22, IT6-F 14/14). The T-ag mRNA was strongly expressed in the gonads, adrenal glands, pituitary, and brain. The KK-1 and KK-3 ovarian tumor cells immunostained with anti-SV40 large-T antibody. The KK-1 cells possessed high-affinity LH receptors [equilibrium association constant (Ka = 7.8 x 10(10) liters/mol] and responded to human CG by elevated cAMP and progesterone production. Also FSH slightly stimulated their cAMP and estradiol production (P < 0.01). These cells expressed cytochrome P450arom and inhibin alpha mRNA, but not cytochrome P450c17 alpha. In conclusion, the KK-1 cells are immortalized luteinizing granulosa cells expressing endogenous gonadotropin receptors, steroidogenic enzymes, and inhibin alpha. These cells will be useful in studies on the molecular aspects of granulosa cell function. The present study indicates that the 6-kilobase fragment of the inhibin alpha promoter described in this article contains the elements directing tissue-specific expression in vivo and is useful for targeted expression of other genes in the gonads.

Activins↗
PubMed1992

The murine luteinizing hormone and follicle-stimulating hormone receptor genes: transcription initiation sites, putative promoter sequences and promoter activity.

The putative promoter regions of the murine follicle-stimulating hormone (FSH) and luteinizing hormone (LH) receptor genes were isolated and used to map transcription initiation sites for both genes. For the FSH receptor gene, a major transcription initiation site was found 534 nucleotides upstream, and for the LH receptor gene 310 nucleotides upstream of the corresponding translation initiation codons. In addition, several alternative minor transcription initiation sites were observed for both genes. The nucleotide sequences of the promoter regions revealed no canonical promoter elements, such as TATA and CCAAT consensus sites 5' of the main transcriptional start sites. The isolated promoter segments for both receptor genes showed low functional activity as verified in transient expression studies in immature rat granulosa cells using the luciferase coding region as the reporter for promoter activity. Both promoter elements seem to be still under tissue specific control, since neither LH receptor nor FSH receptor promoter activity was detectable in another cell line (CHO) investigated.

Amino Acid Sequence↗
PubMed1992

Development of gonadal feedback regulation of gonadotropin gene expression and secretion in female rats.

The postnatal development of the gonadal negative feedback control of gonadotropins was studied in female rats. Neonatal (5-day-old) and randomly cycling young (60-day-old) and more mature (180-day-old) adult rats were ovariectomized, and half of them received Silastic implants containing the synthetic estrogen, diethylstilbestrol. The neonatal rats were killed 5, 10 or 15 days, and the adult rats 7 days after the operation. Age-matched and sham-operated animals served as controls. There were no statistically significant responses of serum LH or FSH concentrations or of the pituitary gonadotropin subunit mRNA levels to ovariectomy at any of the neonatal ages. A marked increase (p < 0.01) after ovariectomy was seen in serum gonadotropins and in the cognate mRNA levels at both adult ages. In spite of the weak feedback response of the neonatal rats to ovariectomy, diethylstilbestrol suppressed the basal pituitary gonadotropin concentrations and the specific LH and FSH beta-chain mRNAs (p < 0.01-0.05). These results demonstrate that the gonadal negative feedback regulation of gonadotropin synthesis and secretion is not fully developed in neonatal and prepubertal female rats before 20 days of age. This is probably due to the steroidogenic quiescence of the ovaries in early life. However, the capability of the pituitary to respond to negative estrogen feedback has developed in the neonatal female, as demonstrated by the suppressive effects of diethylstilbestrol treatment on gonadotropin secretion.

Animals↗
PubMed1992

Ontogeny of gonadotropin action in the rat ovary.

Specific binding of radiolabelled FSH and LH to rat ovaries was demonstrated at the age of 7 days. However, when the biological response to LH and FSH was monitored by cAMP production in vitro, the FSH response appeared earlier than that of LH, on days 4 and 7, respectively. Cholera toxin stimulated cAMP production even in fetal ovaries, suggesting the presence of functional post-receptor machinery of cAMP production. Hence, the appearance of the functional gonadotropin receptor probably plays a key role in the onset of postnatal ovarian steroidogenesis. To test the effect of gonadotropin suppression during postnatal ovarian development, a potent GnRH antagonist was administered to neonatal animals between days 1-6 or 1-9 of life. The ovarian responsiveness to FSH developed even in the absence of normal gonadotropin levels, but that to LH was suppressed after the longer antagonist treatment. The temporal relationship between the onset of LHR gene expression, i.e. transcription, and translation to functional receptor protein was thereafter investigated using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. The measurements revealed the existence only of truncated versions of LHR mRNA in the fetal ovary from day 17 of gestation up to day 7 of postnatal life. With the onset of the receptor function around day 7, also larger mRNA transcripts, corresponding to the full-length receptor protein appeared. Our findings suggest that the LHR gene may be constitutively expressed in the ovary and a change in the alternative splicing pattern may cause the onset of translation of a functional receptor protein.

Animals↗
PubMed1991

Salivary progesterone measurements reveal corpus luteum defects which respond poorly to hormonal treatments in operated mild and moderate endometriosis.

Thirty-five women who had been operated on for mild or moderate endometriosis were evaluated through 40 menstrual cycles by daily measurements of salivary progesterone concentrations. As controls, 17 women with normal ovulatory cycles and no endometriosis were studied. In the endometriosis group, 22 cycles were unstimulated, seven were stimulated by clomiphene citrate and 11 with clomiphene citrate, human menopausal gonadotrophin and human chorionic gonadotrophin. A variety of aberrations in profiles of salivary progesterone secretion was detected in all the groups of endometriosis patients and the frequency of normal cycles was significantly lower than in controls (14-18% versus 82%, P less than 0.01). The response to the treatments varied greatly within the groups. In conclusion, the present data demonstrate that patients with endometriosis have a variety of defects in the menstrual pattern of salivary progesterone secretion and that their corpus luteum function responds poorly to stimulatory treatments.

Adult↗
PubMed1991

Carbohydrate ingestion during prolonged running exercise results in an increase of serum cortisol and decrease of gonadotrophins.

We tested the hypothesis that improved availability of energy through carbohydrate ingestion could counteract the documented suppression of pituitary-gonadal function during prolonged exercise. Nine trained males repeated twice a 36 kilometre running exercise with two weeks interval. During the tests the subjects ingested in a randomized single-blind fashion a total of 1050 millilitres of carbohydrate and placebo solutions. The total amount of ingested carbohydrate was 105 grams. Venous blood samples were taken before the exercise (sample A), immediately after exercise (B), and 2 hours later (C). In the B samples plasma glucose was 14% higher (P less than 0.01) and serum cortisol 13% higher (P less than 0.05) in the carbohydrate than in the control trial. In contrast, the level of LH was 18% (P less than 0.05) and that of FSH 11% lower (P less than 0.05) in the carbohydrate than in the placebo trial. Serum testosterone concentration did not differ between the treatment groups. We conclude that carbohydrate ingestion does not counteract the exercise-associated suppression of gonadotrophin secretion, but results in paradoxical increase of serum cortisol and decrease of LH and FSH, in comparison to placebo-treated controls. The higher cortisol level in carbohydrate group may be secondary to higher insulin levels.

Adult↗
PubMed1990

Gonadotrophin-releasing hormone and human chorionic gonadotrophin tests reveal that both hypothalamic and testicular endocrine functions are suppressed during acute prolonged physical exercise.

The mechanism of suppression of gonadotrophins and testosterone during prolonged exercise was studied. Fourteen healthy males were injected immediately before an exhaustive bicycle run for 4 h, and before a control period without exercise, with one of the following substances: (1) 1 ml of saline, (2) 100 micrograms of a GnRH agonist (buserelin), and (3) 50 IU/kg of hCG. Each test was repeated for each subject 2 weeks apart, in a randomized single-blind fashion. Blood samples were taken before the injections (sample A), 6 h after the injections (sample B), and the following morning (sample C). During placebo treatment testosterone concentration decreased from A samples to B samples more in the exercise trial than in rest trial (31 vs 8%, P = 0.02). This exercise-associated decrease was reversed by both the GnRH agonist and hCG treatments. Serum gonadotrophin concentrations responded identically to GnRH agonist injections during exercise and rest trials. hCG resulted in a greater increase of serum testosterone from A to C samples at rest than during the exercise trial (52 vs 33%, P = 0.04). In conclusion, the exercise-induced suppression of serum testosterone is associated with two effects: suppressed endogenous GnRH stimulation of gonadotrophin release during exercise, and decreased testicular capacity to secrete testosterone during recovery period.

Adult↗
PubMed1988

Serum bioactive and immunoreactive follicle-stimulating hormone in prostatic cancer patients during gonadotropin-releasing hormone agonist treatment and after orchidectomy.

Serum bioactive and immunoreactive FSH levels were measured in five prostatic cancer patients during treatment for 6 months with the GnRH agonist analog buserelin (Hoechst; 600 micrograms, intranasally, 3 times per day) and for up to 12 weeks after subsequent orchidectomy. FSH bioactivity was measured using a sensitive specific in vitro granulosa cells aromatase bioassay. Before buserelin treatment, mean serum FSH bioactivity and immunoreactivity were 19.7 +/- 4.1 (+/- SE) IU/L (n = 5) and 13.7 +/- 3.8 IU/L, respectively, with a bioactivity to immunoactivity (B/I) ratio of 1.7 +/- 0.2. After the initiation of treatment with the GnRH agonist, FSH bio- and immunoactivities both transiently increased for 1-3 days. The increase in bioactivity was greater and prolonged, and the B/I ratio increased nearly 7-fold in 2 weeks. Serum FSH immunoreactivity declined to below the pretreatment level in 5 days and remained low for the rest of the treatment period. In contrast, serum FSH bioactivity did not decrease significantly below the pretreatment level during the 6-month treatment period, although the B/I ratio returned slowly toward the pretreatment value. After orchidectomy, both FSH activities increased dramatically, and the B/I ratio rose transiently from 1.5 to 7 in 2 weeks. Interestingly, serum FSH bioactivity and immunoreactivity decreased significantly (P less than 0.05) 1 day after orchidectomy in the buserelin-treated patients. In contrast, serum FSH immunoreactivity increased during the same period (P less than 0.05) in patients treated only by orchidectomy (FSH bioactivity was not measured). In conclusion, serum FSH bioactivity increases acutely more than FSH immunoreactivity after initiation of GnRH agonist treatment or orchidectomy. In the former case, serum FSH bioactivity subsequently returned to the pretreatment range. A clear decline during long term agonist treatment occurred only in serum FSH immunoreactivity, in contrast to the concomitant decline in serum LH bio- and immunoreactivities reported previously. The persistence of bioactive FSH may explain the inconsistent effects of GnRH agonist treatment on the suppression of spermatogenesis. The acute decrease in serum FSH after orchidectomy in the buserelin-treated men suggests that the testes may produce a factor that stimulates pituitary FSH secretion.

Adult↗
PubMed1987

Blockade of rat testicular gonadotropin releasing hormone (GnRH) receptors by infusion of a GnRH antagonist has no major effects of Leydig cell function in vivo.

The purpose of this study was to examine the physiological functions of the gonadotropin releasing hormone (GnRH) receptors present in the rat testis. The receptors were blocked in situ by infusing one testis of adult rats for 7 days with 10-100 ng/h of a potent GnRH antagonist (N-Ac-Ala1, D-p-Cl-Phe2, D-Trp3,6-GnRH) using Alzet osmotic minipumps. The contents of the pump were delivered to the testis through a cannula perforating, and fixed, to the tunica albuginea. A plastic cannula alone was attached to the contralateral testis, to act as a control. Infusion of the antagonist resulted in a dose-dependent decrease of testicular GnRH receptors, up to 90%. Some of the antagonist also occupied GnRH receptors in the contralateral testis and pituitary, but these effects were always clearly less than in the infused testis. None of the doses used affected circulating levels of gonadotropins, prolactin (Prl) or testosterone. However, when the endocrine parameters of the two testes were compared, the 100 ng/h dose of the antagonist resulted in a significant (P less than 0.01-0.05) 16-32% decrease in the testicular content of testosterone, and LH, FSH and lactogen receptors. Similar effects (inhibition of the same parameters by 22-42%) were observed when immature (30-day-old) male rats were treated for 1 week with intratesticular infusions of the antagonist. It is inferred from these observations that, in physiological circumstances, testicular GnRH receptors may mediate stimulatory effects of Leydig cell LH and lactogen receptors, and testosterone synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Follicle-stimulating hormone receptors appear earlier in the primate fetal testis than in the ovary.

Receptors for FSH as well as FSH-stimulated cAMP production were measured in gonadal tissue of human fetuses of 8-16 weeks gestation and of rhesus monkey fetuses in the last third of gestation. A single population of high affinity receptors (Ka, 1.5-4 X 10(9) M-1) for human FSH was detected in testicular tissue of both species. Specific FSH binding was absent in the human ovaries but present in the two monkey fetal ovaries studied. FSH (1 microgram/mL) did not stimulate cAMP production in slices of any of the gonads studied (human fetal testes and monkey fetal testes and ovaries) or in cultured human granulosaluteal cells used in a control experiment, but FSH increased cAMP 10-fold in immature (10-day-old) rat testes. We conclude that the primate fetal testis, both during the first half and at the end of gestation, may be responsive to FSH stimulation, although this response does not involve the acute elevation of cAMP. In contrast, the absence of FSH receptors in early and midterm human fetal ovaries and the presence of such binding in this tissue in the late gestation monkey indicate that the ovary becomes responsive to FSH stimulation during later stages of fetal development.

Aged↗
PubMed1987

Regulation of LH receptors and steroidogenesis in the foetal rat testis in vivo.

Foetal rats were injected with high doses of hCG or ovine LH (oLH) to determine if LH receptors were down-regulated and steroidogenesis impaired as is seen in the adult animal. Foetuses injected in utero with 52 micrograms/kg hCG had a prompt increase in intratesticular testosterone, demonstrating that the injected substance reached the foetal testis. Pregnant mothers were laparotomized and each foetus in one uterine horn injected with 52 micrograms/kg hCG. Twenty-four hours later, the foetal testes from both uterine horns were collected and free LH receptor content measured. In foetuses injected with hCG, free LH receptors were significantly reduced. LH receptors in foetal testes from the contralateral horn were not significantly different from those in controls. Foetuses injected with 52 micrograms/kg hCG at 17.5 days of gestation showed a delayed response in LH receptor up-regulation when compared with neonatal rats injected with comparable doses of hCG. Injection of foetal and neonatal rats with 400 micrograms/kg oLH showed no evidence of down-regulation, as is seen in the adult. Testes from foetuses injected with 52 micrograms/kg hCG 3 days earlier showed an increase in both basal and hCG-stimulated testosterone production during 3 h of incubation when compared with controls. These results show that the rat foetal testis in vivo does not demonstrate down-regulation of LH receptors or steroidogenic lesions of the testosterone synthetic pathway when exposed to high levels of hCG as does the adult rat testis. These results from the foetal testis in vivo are in agreement with results obtained from the foetal testis in vitro and the neonatal testis in vivo.

Animals↗
PubMed1986

Attenuated adenosine R-site effect in adipocytes in obesity.

Adenosine is a local hormone or a retaliatory metabolite that executes its effect via a plasma membrane receptor, the R-site. In human adipocytes it inhibits cyclic AMP accumulation and lipolysis. N6-(phenylisopropyl)adenosine is a nonmetabolizable derivative that is an R-site agonist not sharing other effects of the parent nucleoside. In subcutaneous abdominal fat cells from obese subjects (130% to 207% of ideal body weight, N = 8), the antilipolytic effect of N6-(phenylisopropyl) adenosine was markedly attenuated as compared to that in fat cells from normal weight subjects (83% to 121% of ideal body weight, N = 8). There was a negative correlation between the effectiveness of the nucleoside analog and the relative body weight of the donor. The effect of N6-(phenylisopropyl)adenosine on cyclic AMP accumulation was similarly attenuated. These findings may explain some of the metabolic alterations observed in obesity.

Adenosine↗
PubMed1986

Effect of postnatal treatment with a gonadotropin-releasing hormone antagonist on sexual maturation of male rats.

The role of postnatal pituitary-testicular activity in sexual maturation at puberty was studied in male rats. Rats were injected twice daily with a potent gonadotropin-releasing hormone antagonist (N-Ac-4-Cl-D-Phe1, 4-Cl-D-Phe2, D-Trp3, D-Phe6, D-Ala10-NH2-GnRH) (GnRH-Ant.), 2 mg/kg, on Days 1-15 of life, and killed on Day 48, 56 or 90 of life. The treatment delayed the onset of puberty (monitored by balano-preputial separation) by 8 days (from the age of 48 to 56 days). The weights of testes, seminal vesicles and ventral prostates were reduced by 50-60% on days 48 and 56 of life, but only the testis weights remained suppressed by Day 90. Levels of serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH), but not those of prolactin (Prl), were elevated 2-to-4-fold in the treated animals at the three ages studied. Serum and testicular testosterone (T) and the receptors for LH and Prl were suppressed in the peripubertal animals (48 and 56 days), but serum T was elevated and the receptor levels were normal in the 90-day group. The testicular FSH receptors were 50% suppressed at all ages studied. Only minor changes were observed in testicular histology when studied at 48 and 56 days. The 85-day-old animals treated with GnRH-Ant. were infertile when mated with females.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Kinetic and autoradiographic studies on binding of hCG to the testicular LH receptors of neonatal rats.

The properties of hCG binding to LH receptors of the neonatal (5-day-old) rat testis were analysed and compared with those of the adult testis. The equilibrium association constants (Ka) of hCG-binding were similar at both ages, 2-4 X 10(10) M-1. In contrast, kinetic binding studies revealed that the association and dissociation rate constants of hCG binding were more rapid in the neonatal testis. Likewise, it was observed that the progression from loose (easily dissociable) to tight (non-dissociable) binding was less complete in the young than in the adult testis. Autoradiography of 125I-labelled hCG binding to interstitial cell suspensions at the two ages showed that the gonadotrophin binding per Leydig cell was about 50% lower in the neonatal testis. Conversely, since the surface area of adult Leydig cells was about 4-fold larger, the receptor density appeared to be higher in the neonatal Leydig cells. The rapid recovery of LH receptors after hCG stimulation, typical of the neonatal cells, was due to rapid replenishment of binding in the cells initially occupied by the injected hormone, rather than to an hCG-induced increase of Leydig cell number. Finally, in-vivo experiments with cycloheximide revealed that the rapid recovery of LH receptors was dependent on protein synthesis. These differences in the kinetics of neonatal testicular LH receptor turnover may be involved in the unique functional features of the fetal-neonatal growth phase of rat testicular Leydig cells.

Animals↗
PubMed1986

Physiological role of putative testicular gonadotrophin releasing hormone (GnRH).

Evidence suggests that exogenous GnRH and agonist analogues have short-term stimulatory effects on rat Leydig cell function - when administered intratesticularly. Since rat Leydig cells possess GnRH receptors and their endogenous ligand has not yet been identified the physiological importance of the observations for testis function is unknown. To address this issue we have determined the consequences of blockade of testis GnRH receptors on Leydig cell function under both normogonadotrophic and hypogonadotrophic stimulation of the testis in vivo. A GnRH antagonist (ANT) was used to achieve receptor blockade but during continuous systemic infusion ANT occupied pituitary GnRH receptors and markedly reduced serum LH, FSH, testosterone, and intratesticular testosterone in adult and 30 d old immature male rats. These results were similar to those obtained by administration of a GnRH antiserum which did not bind to testis GnRH receptors. Thus, blockade of testis GnRH receptors during hypogonadotrophism did not produce additional inhibition of steroidogenesis by Leydig cells. However, direct continuous infusion of ANT into one testis produced greater than 90% occupancy of GnRH receptors while reducing GnRH receptors by only 50% in the contralateral testis. Unilateral intratesticular infusion did not reduce serum LH, FSH, Prolactin or testosterone levels despite 75% occupancy of pituitary GnRH receptors. Thus, both ANT infused and saline infused testes were exposed to the same gonadotrophic stimulants but in the former GnRH-R were essentially non-existent. Compared to the control testis, the ANT infused testis showed a 20-30% reduction in LH, FSH, lactogen receptors and 30-40% fall in testosterone content. Identical results were obtained in adult and 30 d-old male rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Newborn and immature rat testes contain gonadotropin-releasing hormone (GnRH) receptors, and their testosterone production is stimulated by a GnRH agonist in vitro.

The possibility of direct gonadal effects of GnRH in the newborn and immature rat testis was studied by two approaches: the presence of specific high-affinity receptors for a GnRH agonist analogue (Buserelin) was studied in animals between the ages of 1 and 60 days; and the effect of Buserelin on testicular testosterone production was studied in vitro. GnRH receptors were found in the testis tissue at all ages studied, and there was a gradual increase in the number of binding sites per testis with advancing age. The highest concentration of GnRH receptors was found in the rat testis tissue on day 1 of life, 3.2 +/- 0.4 fmoles/g tissue (mean +/- SE, n = 5). The binding declined to a nadir, 1.5 +/- 0.5 fmoles/g tissue (in = 10), on day 15 post-partum (p less than 0.05), and thereafter increased again gradually to a level of 2.7 +/- 0.3 fmoles/g (n = 5) on day 60 of life (p less than 0.05). The biphasic concentration curve of GnRH receptors followed closely the volume density of Leydig cells in the developing rat testis. Buserelin at a concentration of 10(-7) M was able to stimulate significantly (p less than 0.01), by 98-146%, the testosterone production of decapsulated testes at all ages studied between 1 and 60 days of life. These results indicate the presence of functional GnRH receptors in the testis tissue of newborn and immature rats.

Animals↗