New data on a second endogenous molecular form of mammalian hypothalamic LHRH, (hydroxyproline 9) LHRH]

An endogenous hydroxylated form of LHRH, (Hyp) LHRH, is able to displace LHRH bound to pituitary membrane preparations. In parallel, it stimulates release of both LH and FSH from pituitary cells in primary culture. The potency ratio of (Hyp)LHRH is approximately 1:20 and 1:5 with respect to the native decapeptide when peptidasic degradation is or is not inhibited. This correlates with a greater resistance of (Hyp) LHRH towards enzymatic degradation; in contrast to LHRH, the C-terminal (residues 6 to 10) end of (Hyp) LHRH is not degraded and generates C-terminal fragments which account for 64% of the LHRH immunoreactivity in extrahypothalamic areas as the hippocampus. Besides its weak gonadotropin releasing activity and its action or its localization in peripheral organs (placenta, gonads), a major role of the hydroxylated decapeptide may thus be to serve as a precursor of smaller active fragments on targets other than pituitary receptors.     

A synthetic decapeptide analogue of human seminal plasma inhibin exhibiting specific suppression of follicle stimulating hormone release in rats

Synthesis and biological profile of a decapeptide analogue, [Tyr85, Cys(Acm)87]85-94 of human seminal plasma inhibin (HSPI) are described. The peptide suppressed the circulatory levels of follicle stimulating hormone (FSH) in adult male rats. No change in the levels of luteinizing hormone (LH) and prolactin (Prl) was observed. Whereas the peptide suppressed the release of both FSH and LH in vitro. This decapeptide is the smallest peptide reported so far to have FSH suppressing activity.     

Speculations on Structural Relationships between the Hypothalamic Releasing Factors of Pituitary Hormones

RECENTLY, hypothalamic releasing factors have been isolated from two different species (porcine and ovine) and their structures elucidated^1–5. These factors stimulate the secretion of pituitary hormones and have been shown to be small polypeptides. Thyrotropin releasing factor (TRF) for both species is the tripeptide pyroglutamyl-histidyl-proline amide (pGlu-His-Pro-amide)^1,2. TRF acts on pituitary thyrotrophs to stimulate the secretion of thyroid stimulating hormone (TSH). The structure of a hypothalamic factor which stimulates the secretion of the pituitary gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH) has been determined. This gonadotropin releasing factor, referred to as LRF, is a decapeptide and, like TRF, has both terminals blocked; in both species its primary sequence is pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-amide^3–5.     

Triiodothyronine (T3) modulation of gonadotropin secretion in the female rat.

The effect of T3 upon gonadotropin secretion was examined in ovariectomized (Ovarx), Ovarx thyro-parathyroidectomized (Ovarx-TxPx), or proestrus rats. T3 (50 microgram/-100 gBW), administered late diestrus-2, abolished the LH surge during the critical period of proestrus in 7 out of 9 rats; the rise in sera FSH was not inhibited, although a distinct peak was absent. Administration of 5 or 50 microgram T3/100gBW 2.5h before the critical period resulted in either a suppression or an alteration of the timing of LH release. In the 5 microgram T3/100gBW treated animals the sera FSH peak was delayed in timing, whereas in the 50 microgram T3/100gBW treated rats sera FSH demonstrated two separate peaks during the critical period. Treatment with various dosages of T3 of Ovarx-TxPx rats resulted in significant suppressions (p less than 0.05) of sera LH and FSH. Despite depressed concentrations of sera LH and FSH in T3-treated rats pituitary sensitivity to a challenge of 3LHRH was enhanced. Hence, the pituitary was not the site of T3 inhibition of gonadotropin secretion. Additionally, T3 did not modify pituitary LH content or hypothalamic LH3 releasing activity (LHRH). Since T3 did not inhibit gonadotropin secretion at the pituitary level, a neural site of T3 action is suggested.     

Radioimmunoassay of luteinizing hormone in the baboon (Papio hamadryas)

A heterologous radioimmunoassay (RIA) for luteinizing hormone (LH) consisting of a cynomolgus LH tracer and an antiserum raised against human chorionic gonadotropin (cynLH:anti-hCG) fulfilled the recognized criteria of reliability when applied to baboon (Papio hamadryas) plasma and pituitary extracts obtained in different endocrine conditions. This RIA is 5.5 times more sensitive than the ovine (oLH:anti-oLH) system, yields estimates of baboon LH (bLH) fairly close to those obtained by in vitro bioassay, and recognizes all bioactive molecular species of bLH present in male and female pituitary extracts. However, the system yields slightly but significantly lower estimates of bLH than the in vitro bioassay.     

Conformation of an analog of human follicular gonadotropin releasing peptide TF14 in solution by 2D-NMR

Since the discovery of hF-GRP, several analogs have been synthesized in order to see their effects on the gonadotropin releasing activity, either as agonists or antagonists to this peptide. TF14 is one of these analogs, whose 14th position in the primary sequence is Phe instead of Asn in hF-GRP, while its activity is doubled. 2D-NMR (TOCSY, ROESY) was used to determine the conformation of TF14 in solution. Compared with hF-GRP, the whole peptide is in a non-typical more extended conformation, which may give some due to the relation between structure and function of these two peptides.     

Differential actions of GnRH and rat hypothalamic extracts in release of hypophysial FSH and LH in vitro.

A study was made of the separate patterns of luteinizing hormone (LH) and follicle stimulating hormone (FSH) release from isolated rat pituitary tissue evoked by synthetic gonadotropin releasing hormone (GnRH) or female hypothalamic extracts (HE), respectively, in a continuous perifusion system. Under defined conditions, gonadotropin release from hemipituitaries was relatively stable and reproducible. Absolute levels of LH and FSH release evoked by HE in terms of their GnRH content were always greater than those following exposure to synthetic GnRH at varying doses. Synthetic GnRH released more FSH than LH. In contrast, the HE released slightly higher levels of LH than FSH. The data suggest that the female rat hypothalamus contains substances other than GnRH, capable of releasing both LH and FSH. It is possible that such unidentified components can modify the hypophysial action of GnRH, resulting in particular circumstances in a differential release of LH and FSH.     

Experimental data supporting the expression of the highly conserved GnRH-II in the brain and pituitary gland of rats

The second GnRH form, originally identified in chickens (cGnRH-II or GnRH-II), is the most ubiquitous peptide of the GnRH neuropeptide family, being present from jawed fish to human beings. However, the presence of GnRH-II in such an important experimental model as the rat is still an object of discussion. Here we present chromatographic, immunologic and biologic activity evidence supporting the expression of GnRH-II in the rat. Olfactory bulb, hypothalamus, remnant brain and anterior pituitary from a pool of 50 female adult rats were extracted and subjected to RP-HPLC on a C-18 column. The fractions were collected and evaluated by using two different RIA systems, specific for GnRH-I and GnRH-II respectively. Under these conditions the GnRH-I standard eluted in fraction 21 (f21) was only detected with the GnRH-I RIA system, whereas the GnRH-II standard was only detected in the fraction 27 (f27) by using a GnRH-II RIA system. In the olfactory bulbs extract, the fractions analyzed by the GnRH-I RIA systems showed a single peak in f21, whereas by using the GnRH-II RIA system a single peak at f27 was observed. In the hypothalamus GnRH-I was detected in f21 meanwhile GnRH-II could not be detected. When the remnant brain and pituitary gland extracts were analyzed, both GnRH forms were detected. To the best of our knowledge, this is the first report concerning GnRH-II detection in a mammalian pituitary. Serial dilutions of f27 and GnRH-II presented similar displacement of radioiodinated-GnRH-II, demonstrating that both molecules share immunological properties. Moreover, after 60 min stimulation, both f27 and GnRH-II had similar LH and FSH releasing activity in 12 day-old rat pituitary primary cell cultures. However, we failed to characterize the GnRH-II gene in this model. These results provide strong evidence for the expression of GnRH-II in the rat brain and pituitary gland.     

Luteinizing Hormone and Follicle Stimulating Hormone-Releasing Hormone Test in Patients with Hypothalamic Pituitary-Gonadal Dysfunction

A standard intravenous 100 μg luteinizing hormone/follicle stimulating hormone-releasing hormone (LH/FSH-RH) test was used to assess the pituitary gonadotrophin responses in 155 patients with a variety of diseases of the hypothalamic-pituitary-gonadal axis. In all but nine patients there was an increase in circulating levels of either LH or FSH in response to the releasing hormone though 137 (88%) were clinically hypogonadal. It was not possible with this test to distinguish between hypothalamic and pituitary causes of hypogonadotrophic hypogonadism, since a variety of LH and FSH responses emerged within the disease groups. However, primary gonadal failure characteristically resulted in exaggerated gonadotrophin response. The potential therapeutic use of the gonadotrophin releasing decapeptide is suggested in certain patients with hypogonadotrophic hypogonadism.     

The similarity of FSH-releasing factor to lamprey gonadotropin-releasing hormone III (l-GnRH-III)

To validate further the existence of a specific hypothalamic follicle stimulating hormone releasing factor (FSHRF), stalk-median eminence (SME) fragments from sheep and whole hypothalami from male rats were purified by gel filtration on Sephadex G-25, and the gonadotropin-releasing activity on hemipituitaries of rats incubated in vitro was determined by bioassay and compared with the radioimmunoassayable luteinizing hormone releasing hormone (LHRH) and lamprey gonadotropin releasing hormone (l-GnRH) activities in the fractions. The FSH-releasing fractions eluted in the same sequence of tubes from the Sephadex column found earlier by in vivo bioassay and were clearly separated from the immunoassayable and bioassayable LHRH. The radioimmunoassay (RIA) for l-GnRH recognized equally l-GnRH-I and -III but had negligible cross-reactivity with LHRH. Fractionation of rat hypothalamic extract by gel filtration on Sephadex G-25 revealed three peaks of l-GnRH determined by RIA, all of which eluted prior to the peak of LHRH. Only the second peak had FSH-releasing but not LH-releasing activity. To determine if this FSH-releasing activity was caused by the presence of l-GnRH in the fraction, the pituitaries were incubated with normal rabbit serum or the l-GnRH antiserum (1:1000), and the effect on the FSH- and LH-releasing activity of the FSH-releasing fraction and the LH-releasing activity of LHRH was determined. The antiserum had no effect on basal release of either FSH or LH but eliminated the FSH-releasing activity of the active fraction without altering the LH-releasing activity of LHRH. Since l-GnRH-I has little activity to release FSH or LH, and its activity is nonselective, whereas previous experiments have shown that l-GnRH-III highly selectively releases FSH with a potency equal to that of LHRH to release LH, the results support the hypothesis that the FSH-releasing activity observed in these experiments was caused by l-GnRH-III or a closely related peptide.     

Partial purification and characterization of rhinoceros gonadotropins, growth hormone, and prolactin: comparison with the horse and sheep

The rhinoceros is an endangered species related to the horse family. Little is known of its reproductive endocrinology. The objectives of this study were to partially purify rhinoceros pituitary hormones, determine which assays could be used for their assessment, and to ascertain whether rhinoceros LH possesses the intrinsic FSH activity of equine LH. A single pituitary each from a White (1.3 g) and a Black (1.2 g) Rhinoceros was homogenized and extracted (pH 9.5), then subjected to pH and salt fractionation, and ion-exchange chromatography (DEAE and Sephadex SP-C50) to yield partially purified fractions of LH, FSH, growth hormone (GH), and prolactin (PRL). LH was readily measured by a rat Leydig cell assay (0.1-1% x equine LH) and an RIA using a monoclonal antibody to bovine LH (6-11% x equine LH). FSH activity detected in the LH by either an FSH RIA or a calf testis radioreceptor assay (RRA) was extremely low. No FSH activity could be detected in the White Rhinoceros pituitary "FSH" fraction, but was readily detected in the Black Rhinoceros fraction (RIA: 0.2% x equine FSH: RRA: 0.8% x equine FSH). The presence of GH and PRL was determined by SDS-PAGE and Western blots. Results showed a single immunoreactive GH band and multiple immunoreactive PRL bands. Adsorption with Concanavalin A-Sepharose indicated that some of the PRL bands are glycosylated.     

Effect of porcine gastrin releasing peptide on anterior pituitary hormone release

The effect of porcine gastrin releasing peptide (GRP), a heptacosapeptide with potent gastrin releasing activity which has recently been isolated from porcine non-antral gastric tissue, on pituitary function was investigated in the rat. Graded doses of synthetic porcine GRP were injected intravenously and the animals were killed at various intervals after injection. Growth hormones, LH, FSH, and TSH were measured in serum by specific radioimmunoassays. GRP had no significant effect on growth hormone or FSH serum concentrations at any dose or sampling time studied. In contrast, the heptacosapeptide significantly stimulated LH and suppressed TSH secretion in a dose-related fashion. Since there are striking structural similarities between GRP and bombesin, a tetradecapeptide from amphibian skin which shows amino acid homology with the C-terminal region of GRP, GRP may be the mammalian counterpart of bombesin.     

Relation between levels of circulating ovarian steroids and pituitary gonadotropin content during the menstrual cycle of the rhesus monkey

Anterior pituitary glands were removed from 27 intact cycling rhesus monkeys sacrificed in the early (Day 2), mid (Days 6--9) and late (Days 11--12) follicular phase, and in the early and late luteal phase (3--5 and 10--15 days after the midcycle luteinizing hormone (LH) surge). Assignment of cycle stage was confirmed by the pattern of circulating steroid and gonadotropin levels seen in the blood samples taken daily throughout the cycle. The anterior pituitary glands were weighed, stored at -30 degrees C and assayed for LH and follicle-stimulating hormone (FSH) content by specific radioimmunoassays. Serum estradiol levels and pituitary LH and FSH contents rose simultaneously during the follicular phase. After the preovulatory gonadotropin surge, pituitary LH content was low and invariant. Pituitary FSH content reached a nadir in the early luteal phase and tended to rise in the late luteal phase. Multiple correlation analyses revealed that there is a positive correlation between rising levels of estradiol in the circulation and pituitary LH (p = 0.003) and FSH (p = 0.017) content, and that there is a significant negative correlation between circulating progesterone levels and pituitary FSH content (p = 0.002). Pituitary LH content is less strongly related to circulating progesterone levels. There was no significant difference in the wet weights of the anterior pituitary glands during the five phases of the menstrual cycle studied.     

Generation of hypophysiotropic activity in hypothalamic extracts in vitro.

The luteinizing hormone (LH) and follicle stimulating hormone (FSH) releasing activity, as well as the prolactin (PRL) release-inhibiting activity were measured in both neutral aqueous, and acid ethanolic extracts of rat hypothalami. LH and FSH-releasing activities were detectable only in the latter type of extract, whereas PRL release-inhibiting activity appeared in both. Neutral ultrafiltrates of the neutral extracts contained no gonadotropin releasing activity, however, acidification of the filtration medium induced its appearance. PRL release was inhibited by both neutral and acid filtrates. These results suggest that LH and FSH releasing factor(s) may be stored in the hypothalamus in an inactive form from which the active peptide is generated in vitro under acid conditions; however, this does not appear to be true for the component(s) responsible for the inhibition of PRL release.     

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)     

乙炔基雌二醇(EE2)对雄性黄颡鱼GtH3个亚基基因表达的影响

为研究乙炔基雌二醇(EE2)是否能影响雄性黄颡鱼(Pelteobagrus fulvidraco)垂体中促性腺激素3个亚基基因的表达,从而干扰FSH和LH的分泌,研究采用末端快速扩增(RACE)的方法在黄颡鱼垂体中克隆了促性腺激素的2个亚基(FSH和LH)的全长cDNA,对其组织表达模式和雌雄性垂体中的季节表达模式进行了研究;另外,研究还用100 ng/L的EE2对雄性黄颡鱼(2龄)进行了28d的暴露处理。结果发现,黄颡鱼FSH cDNA全长528 bp, ORF为399 bp,编码132个氨基酸; LH全长为870 bp, ORF为417 bp,编码138个氨基酸。序列分析结果表明,黄颡鱼FSH含有一个17氨基酸的信号肽, 2个保守的N-糖基化位点和13个半胱氨酸残基,而LH含有一个18个氨基酸的信号肽, 1个N-糖基化位点和12个半胱氨酸残基,与其他鲶形目鱼类极其相似。进化分析显示,黄颡鱼FSH和LH与鲶形目的鱼类进化关系较近。组织分布结果发现,黄颡鱼3亚基均仅在垂体中表达。季节表达模式结果表明,雌雄黄颡鱼GtH和LH表达水平在5月份左右达到最高,随后降低; FSH在雌性的表达模式与GtH和LH相同,而在雄性, FSH的表达没有明显变化。半定量RT-PCR结果显示, 100 ng/L的EE2能显著抑制黄颡鱼促性腺激素3个亚基基因的表达。研究认为, EE2抑制黄颡鱼雄性垂体FSH和LH的分泌,可能阻碍其正常的精子发生、精子成熟和排精过程,从而影响其正常的繁殖和发育。       

Photoaffinity labeling of pituitary GnRH receptors: significance of the position of photolabel on the ligand

Photoreactive derivatives of GnRH and its analogues were prepared by incorporation of the 2-nitro-4(5)-azidophenylsulfenyl [2,4(5)-NAPS] group into amino acid residues at positions 1, 3, 6, or 8 of the decapeptide sequence. The modification of Trp3 by the 2,4-NAPS group led to a complete loss of the luteinizing hormone (LH) releasing as well as LH-release-inhibiting activity of the peptide. The [D-Lys(2,4-NAPS)]6 analogue was a very potent agonist that, after covalent attachment by photoaffinity labeling, caused prolonged LH secretion at a submaximal rate. [Orn(2,4-NAPS)]8-GnRH, a full agonist with a relative potency of 7% of GnRH, after photoaffinity labeling caused prolonged maximal LH release from cultured pituitary cells. In contrast, [Orn(2,5-NAPS)]8-GnRH, although being equipotent with the 2,4-NAPS isomer in terms of LH releasing ability, was unable to cause prolonged LH release after photoaffinity labeling. Thus, [Orn(2,4-NAPS)]8-GnRH is a very effective photolabeling ligand of the functionally significant pituitary GnRH receptor. Based on this compound, a pituitary peptidase resistant derivative, D-Phe6,[Orn(2,4-NAPS)]8-GnRH-(1-9)-ethylamide, was synthesized. This derivative showed high-affinity binding to pituitary membranes with a Kd comparable to those of other GnRH analogues. A radioiodinated form of this peptide was used for pituitary GnRH-receptor labeling. This derivative labeled 59- and 57-kDa proteins in rat and 58- and 56-kDa proteins in bovine pituitary membrane preparations, respectively. This peptide also labeled pituitary GnRH receptors in the solubilized state and therefore appears to be a suitable ligand for the isolation and further characterization of the receptor.     

Preparation and characterization of photoreactive derivatives of GnRH. Persistent activation of function by photoaffinity labeling

A photoreactive derivative of the highly potent gonadotropin releasing hormone (GnRH) agonist, D-Lys6-GnRH(1-9)-ethylamide, was prepared by selective modification of the epsilon-amino group with 2-nitro-4-azidophenyl sulfenyl chloride (2,4-NAPS C1). The modified peptide [D-Lys(NAPS)]6-GnRH-(1-9)-ethylamide was found to be a full agonist of LH release from rat pituitary cells with a relative potency 23 compared to GnRH. Covalent attachment of the photoreactive analog to rat pituitary cells resulted in prolonged activation of LH secretion which could not be inhibited by a potent GnRH antagonist. Persistent stimulation of pituitary gonadotrophs caused by covalently bound hormone led to desensitization of the LH releasing mechanism.     

Dependence of secretory responses to gonadotropin-releasing hormone on diacylglycerol metabolism. Studies with a diacylglycerol lipase inhibitor, RHC 80267

The role of diacylglycerol (DG) as a source of arachidonic acid during gonadotropin-releasing hormone (GnRH) stimulation of gonadotropin secretion was analyzed in primary cultures of rat anterior pituitary cells. An inhibitor of DG lipase (RHC 80267, RHC) caused dose-dependent blockade of GnRH-stimulated luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. The DG lipase inhibitor did not alter gonadotropin responses to arachidonic acid, and addition of arachidonic acid reversed its inhibition of GnRH-stimulated LH and FSH release. In [3H]arachidonic acid-prelabeled cells, incubation with RHC increased the accumulation of [3H]DG. These results suggest that DG lipase participates in GnRH action and that arachidonic acid mobilization from DG is involved in the mechanism of gonadotropin release. Gonadotropin responses to tetradecanoyl phorbol acetate and dioctanoyl glycerol were not altered by RHC, and the addition of these activators of protein kinase C (Ca2+- and phospholipid-dependent enzyme) did not prevent the inhibition of GnRH-induced gonadotropin release by RHC. Activation of phospholipase A2 by melittin increased LH and FSH secretion, whereas blockade of this enzyme by quinacrine reduced GnRH-stimulated hormone release. However, RHC did not diminish the gonadotropin response to melittin. The inhibitory actions of RHC and quinacrine were additive and were reversed by concomitant treatment with arachidonic acid. Ionomycin also increased LH and FSH release, and the gonadotropin responses to the ionophore were unaltered by RHC but were reduced by quinacrine. Incubation of cells in Ca2+-depleted (+/- [ethylenebis(oxyethylenenitrilo)]tetraacetic acid) medium reduced but did not abolish the LH and FSH releasing activity of GnRH. Treatment with RHC also reduced the gonadotropin responses to GnRH under Ca2+-depleted conditions. These observations indicate that RHC inhibition of GnRH action is not due to nonspecific actions on Ca2+ entry, protein kinase C activation and actions, nor phospholipase A2 enzyme activity. The results of this study provide further evidence for an extracellular Ca2+-independent mechanism of GnRH action, and suggest that GnRH causes mobilization of arachidonic acid by two distinct lipases, namely, phospholipase A2 and DG lipase, during stimulation of gonadotropin secretion.     

Differential regulation of pituitary gonadotropin subunit messenger ribonucleic acid levels in photostimulated Siberian hamsters

FSH levels begin to rise 3-5 days after male Siberian hamsters are transferred from inhibitory short photoperiods to stimulatory long photoperiods. In contrast, LH levels do not increase for several weeks. This differential pattern of FSH and LH secretion represents one of the most profound in vivo examples of differential regulation of the gonadotropins. The present study was undertaken to characterize the molecular mechanisms controlling differential FSH and LH synthesis and secretion in photostimulated Siberian hamsters. First, we cloned species-specific cDNAs for the three gonadotropin subunits: the common alpha subunit and the unique FSHbeta and LHbeta subunits. All three subunits share high nucleotide and predicted amino acid sequence identity with the orthologous cDNAs from rats. We then used these new molecular probes to examine the gonadotropin subunit mRNA levels from pituitaries of short-day male hamsters transferred to long days for 2, 5, 7, 10, 15, or 20 days. Short-day (SD) and long-day (LD) controls remained in short and long days, respectively, from the time of weaning. We measured serum FSH and LH levels by RIA. FSHbeta, LHbeta, and alpha subunit mRNA levels were measured from individual pituitaries using a microlysate ribonuclease protection assay. Serum FSH and pituitary FSHbeta mRNA levels changed similarly following long-day transfer. Both were significantly elevated after five long days (2.3- and 3.6-fold, respectively; P < 0.02) and declined thereafter, but they remained above SD control values through 20 long days. Alpha subunit mRNA levels also increased significantly relative to SD control values (maximum 2-fold increase after seven long days; P < 0.03), although to a lesser extent than FSHbeta. Neither serum LH nor pituitary LHbeta mRNA levels changed significantly following long-day transfer. The results indicate that long-day-associated increases in serum FSH levels in Siberian hamsters reflect an underlying increase in pituitary FSHbeta and alpha subunit mRNA accumulation.