Replicating viral vectors as HIV vaccines: summary report from the IAVI-sponsored satellite symposium at the AIDS vaccine 2009 conference.

In October 2009, The International AIDS Vaccine Initiative (IAVI) convened a satellite symposium entitled 'Replicating Viral Vectors for use in AIDS Vaccines' at the AIDS Vaccine 2009 Conference in Paris. The purpose of the symposium was to gather together researchers, representatives from regulatory agencies, and vaccine developers to discuss issues related to advancement of replication-competent viral vector- based HIV vaccines into clinical trials. The meeting introduced the rationale for accelerating the development of replicating viral vectors for use as AIDS vaccines. It noted that the EMEA recently published draft guidelines that are an important first step in providing guidance for advancing live viral vectors into clinical development. Presentations included case studies and development challenges for viral vector-based vaccine candidates. These product development challenges included cell substrates used for vaccine manufacturing, the testing needed to assess vaccine safety, conducting clinical trials with live vectors, and assessment of vaccination risk versus benefit. More in depth discussion of risk and benefit highlighted the fact that AIDS vaccine efficacy trials must be conducted in the developing world where HIV incidence is greatest and how inequities in global health dramatically influence the political and social environment in developing countries.

Induction of specific CD8+ T-lymphocyte responses using a human papillomavirus-16 E6/E7 fusion protein and autologous dendritic cells.

When intracellular viral proteins are degraded, only a limited number of peptide epitopes are capable of eliciting specific CD8+ cellular immune responses for a given human leukocyte antigen (HLA) haplotype. We sought to induce CD8+ T-lymphocyte (CTL) responses to human papillomavirus-16 (HPV-16) E6 and E7 proteins using a recombinant E6/E7 fusion protein and autologous human dendritic cells (DCs). CTLs were generated by in vitro stimulation using a recombinant HPV-16 E6/E7 fusion protein and autologous DCs from a healthy HLA-A*0201 donor. CTL specificity was assessed by cytokine release assays when the cells were reacted with autologous DC targets coincubated with the E6/E7 fusion protein. These CTLs were also reacted with the immunodominant E7 peptides (E711-20 and E7(86-93)) and DCs as a target. As a negative control, DCs were incubated with or without an irrelevant control protein (Helicobacter pylori) as target for the E6/E7-induced CTLs. The E6/E7-induced CTLs were capable of specific recognition of target DCs coincubated with E6/E7 but not the control protein. When E6/E7-specific CTLs were reacted with DCs and either E7(11-20) or E7(86-93), specific peptide recognition was also detected. These data demonstrate that specific CTLs can be elicited using autologous human DCs and a HPV-16 E6/E7 fusion protein. Therefore, extracellular viral proteins seem to be engulfed and processed by DCs; then the immunodominant HLA-A2-restricted peptides become available for CD8+ T-lymphocyte recognition. These data suggest that vaccine strategies using recombinant viral proteins may overcome the limitation of peptide epitopes for specific HLA haplotypes and may, therefore, permit more generalized clinical application.

Expression of ovarian inhibin during pregnancy in the rat.

We have examined the expression of the rat inhibin genes in the maternal ovary during pregnancy. RNA blot analysis indicates that the inhibin-alpha chain mRNA is expressed in the ovary throughout gestation at levels comparable to those observed in cycling rats. In situ hybridization shows that the inhibin-alpha and -beta A mRNAs are produced in the granulosa cells of developing antral follicles; little or no hybridization to functional corpora lutea is observed. Early in pregnancy, a large number of follicles hybridize to both alpha- and beta A-inhibin cDNA probes. Many of these follicles undergo atresia during the first half of pregnancy, and the number of inhibin-expressing follicles reaches a nadir on day 15. This is followed by an increase in inhibin-producing follicles, which peaks just before parturition. The increase in inhibin-expressing follicles observed in late pregnancy corresponds to a small rise in serum inhibin levels, as measured using an alpha chain-specific RIA. After the first postpartum ovulation, few hybridizing follicles are observed. Ovariectomy in either early (day 6) or mid (day 15) pregnancy results in a significant fall in serum inhibin levels and a robust increase in serum FSH levels 9 h after surgery. These results suggest that inhibin is produced by the maternal ovary during pregnancy, that its synthesis is modulated during late gestation, and that inhibin may play a role in regulating FSH secretion during pregnancy.

Developmental hormonal profiles accompanying the neonatal hypothyroidism-induced increase in adult testicular size and sperm production in the rat.

Neonatal treatment with the reversible goitrogen 6-N-propyl-2-thiouracil (PTU) results in a near doubling of testicular size and a 25% increase in the efficiency of spermatogenesis, without affecting circulating testosterone (T) levels in adult rats. The objectives of the present study were to examine the effects of neonatal PTU treatment on the pattern of testicular growth and circulating levels of anterior pituitary (FSH, LH, PRL, GH, and TSH), gonadal [immunoreactive inhibin-alpha (irI alpha) and T], and thyroid (T3 and T4) hormones over the first 100 days of life. Treatment of rats with PTU from birth to 24 days of age significantly reduced testicular weights between 10 and 60 days of age. However, the duration of testicular growth was extended in treated males, resulting in a 68% increase at 100 days of age. Serum gonadotropin levels in treated males were reduced throughout the experimental period, typically remaining between 50-70% of control levels. The characteristic robust prepubertal FSH peak was absent in PTU-treated males. Initially high until 20 days of age, irI alpha levels characteristically declined to adult levels (200-300 pg/ml) in control males. In treated males, irI alpha levels were reduced during the period of hypothyroidism, increased between 30 and 60 days, and then declined, but remained significantly higher (1.7- to 2-fold greater) than those observed in control males. Serum T levels were similar in treated and control males. Control males demonstrated increased T levels beginning at 45 days of age, earlier than observed in treated males; however, similar peak T levels were observed in all males. PTU treatment significantly suppressed serum GH and PRL and led to a 14-fold increase in circulating TSH during the period of treatment. However, unlike the gonadotropins, these hormones returned to control levels after PTU treatment, suggesting that the reduced levels of FSH and LH observed are not due to a generalized reduction in pituitary function. Serum T4 and T3 levels returned to control levels within 15 days after the removal of PTU. These results demonstrate that the neonatal PTU treatment-induced increases in adult testicular size and sperm production were not due to increased levels of FSH at any point in development. On the contrary, the observed increases occur in spite of chronically reduced FSH levels.

Corticotrophin-releasing factor-like immunoreactivity and bioactivity of human fetal and adult hypothalami.

Corticotrophin releasing factor-like immunoreactivity (CRF-LI) and bioactivity, and arginine vasopressin-like immunoreactivity (AVP-LI) have been measured in extracts of human fetal and adult hypothalamic tissue and their development with the gestational age of the fetuses (12-27 weeks) studied. CRF-LI was measured by a radioimmunoassay developed for ovine corticotrophin-releasing factor (oCRF-41). Corticotrophin-releasing factor bioactivity was measured in a rat isolated anterior pituitary cell perfusion system. CRF-LI and bioactivity and AVP-LI were all detectable in fetal hypothalamic extracts from 12 to 13 weeks of gestational age. CRF-LI was also present in human fetal pituitary glands from 12 weeks of gestational age. The concentration of CRF-LI in the fetal hypothalamic extracts (9.2 +/- 11.4 ng/g, mean +/- S.E.M., n = 33) showed no significant correlation with the gestational age of the fetuses. However the concentration of AVP-LI (25.0-36.8 ng/g, n = 17) did show a positive correlation (r = 0.508, P less than 0.05) with gestational age, as did the concentration of CRF bioactivity (471.3-556.3 ng ACTH released/g tissue, n = 13, r = 0.725, P less than 0.01). The CRF bioactivity of all fetal hypothalamic extracts was potentiated by the addition of synthetic human (h)AVP, but the bioactivity of the adult hypothalamic extracts was not, presumably because of the higher levels of AVP-LI already present in the adult extracts. Pretreatment of tissue extracts with antisera to oCRF-41 and/or hAVP reduced the CRF bioactivity of all hypothalamic extracts. Sephadex chromatography of fractions which co-eluted with synthetic oCRF-41 or hAVP contained CRF bioactivity and this bioactivity was potentiated when synthetic hAVP or oCRF-41, respectively, were added to the fractions. However, a larger molecular weight form of CRF-LI (8000-10 000 daltons), which was observed only in fetuses of 20 weeks of gestational age or less, did not contain any significant CRF bioactivity.

Corticotrophin-releasing factor--mediated adrenocorticotrophin release from rat anterior pituitary cells is potentiated by C-terminal gastrin-releasing peptide.

The remission of Cushing's syndrome following surgical removal of a tumour containing bombesin-like immunoreactivity (BLI), but insignificant levels of ACTH, is described. However, an acid extract of the tumour tissue caused the release of ACTH from isolated rat anterior pituitary cells in vitro. These observations led to an investigation of the effects of synthetic C-terminal gastrin-releasing peptide (GRP(14-27] on ACTH release from isolated rat anterior pituitary cells. GRP(14-27) (10-1000 ng/ml) directly stimulated the release of ACTH in vitro, whereas lower doses (10-1000 pg/ml), ineffective themselves in eliciting ACTH release, potentiated the CRF-mediated in-vitro release of ACTH.

Partial purification and characterization of a novel growth hormone-releasing factor (GRF) from teleost brain related to the rat hypothalamic peptide.

A growth hormone-releasing factor (GRF)-like molecule has been partially purified and characterized from acid extracts of codfish (Gadhus morhua) brain using immunoaffinity and gel chromatography, followed by HPLC. This material has a mol.wt. which is similar to known mammalian forms of GRF but is immunologically and/or chromatographically distinct from previously described GRF peptides. However, it is related to rat(r) GRF(1-43) since it causes marked displacement in the rGRF RIA. Codfish GRF is a highly specific and potent hypophysiotropic factor as shown by its ability to stimulate the release of GH, but no other hormone, from rat anterior pituitary cells in vitro. These findings suggest that, phylogenetically, GRF is an ancient molecule with its biologic activity and certain immunoreactive domain(s) conserved, at least, from teleost to mammal.

Purification and characterization of luteinizing hormone-releasing hormone from codfish brain.

We have purified luteinizing hormone-releasing hormone (LH-RH) from codfish brain and have demonstrated its identity with salmon LH-RH (sLH-RH). An antiserum raised against sLH-RH was used in a specific radioimmunoassay (RIA) to monitor purification and to manufacture an immunoaffinity chromatography column for the initial purification step. The cross-reactivity of the sLH-RH RIA with mammalian LH-RH was 0.1%. Acid extracts of codfish brains were sequentially purified by immunoaffinity chromatography, gel-filtration chromatography, and three steps of reverse-phase HPLC. The purified material and synthetic sLH-RH coeluted on reverse-phase HPLC and exhibited similar biological activity in a dispersed pituitary cell bioassay. Furthermore, the amino acid composition of the purified material was identical to salmon LH-RH. These results suggest that there is structural conservation of LH-RH between these species of teleost fish.

Characterisation of immunoreactive somatostatin in human fetal hypothalamic tissue.

Levels of immunoreactive somatostatin (IRS) were measured in extracts of hypothalamic tissue from human fetuses of 12-26 weeks gestation. The IRS contents (0.7-22.5 ng) and concentrations (2.7-118.0 pg/mg wet weight tissue) both increased slightly with gestation. Sephadex G-50 chromatography of 11 extracts showed up to four peaks of IRS, one co-eluting with synthetic somatostatin-14 (S14), a second co-eluting with synthetic somatostatin-28 (S28) and two other peaks having approximate molecular weights of 6000 and 10 000, respectively. The levels of S14 and S28 increased significantly during gestation, while the levels of 6000 molecular weight IRS decreased with age. We suggest that the increase in S14 and S28 levels may be the cause of the fall in circulating growth hormone (GH) in the fetus in later gestation.

Replicating viral vectors as HIV vaccines Summary Report from IAVI Sponsored Satellite Symposium, International AIDS Society Conference, July 22, 2007.

At the International AIDS Society Conference on Pathogenesis, Treatment and Prevention held in Sydney, Australia, in July 2007, the International AIDS Vaccine Initiative (IAVI) convened a satellite symposium entitled 'Accelerating the Development of Replicating Viral Vectors for AIDS Vaccines.' Its purpose was to highlight the rationale for accelerating the development of replicating viral vectors for use as vaccines against HIV-1, and to bring together vaccine scientists, regulatory officials, and public health specialists from industrialized and developing nations to discuss the major issues facing the development and testing of replicating viral vector-based vaccines.

Recombinant NY-ESO-1 cancer antigen: production and purification under cGMP conditions.

The cancer-testis antigen, NY-ESO-1, has been engineered into a bacterial expression plasmid which incorporates a His6-tag. The plasmid was transfected into E. coli strain BL21 and Master and Working cell banks generated from this expression system. Three 15-litre fermentations were performed under cGMP (code of Good Manufacturing Practice) conditions and the crude NY-ESO-1 tagged protein isolated as solubilised inclusion bodies. A three-step cGMP chromatography process (immobilised metal affinity, anion exchange, and hydrophobic interaction) was utilised to purify the protein. The purified NY-ESO-1 is being used in early stage human cancer vaccine trials in Australia and the U.S.A.

Changes in serum immunoreactive inhibin and follicle-stimulating hormone during gonadal development in male and female rats.

We have measured serum and ovarian immunoreactive inhibin alpha (irI alpha) and serum FSH in fetal and neonatal rats from 20 days of gestation until 40 days of age. For animals aged 10 days or older, serum measurements were made on intact and gonadectomized animals. Serum irI alpha was detectable in intact male and female rats at all ages studied. In females, irI alpha levels were low until Day 5 and then increased steadily to peak at Day 25. Thereafter they declined until Day 35 to reach levels typical of adult females. There was a significant decrease in irI alpha levels 24 h after ovariectomy at all ages. Serum FSH levels in females were low until Day 7, then increased rapidly to plateau from Days 10-15. The levels then declined until Day 25 and were generally unchanged after that time. There was a significant increase in FSH 24 h after ovariectomy in rats aged 20 days and older, and in younger rats by 48 h after ovariectomy. In male rats, serum irI alpha levels were significantly higher than females until Day 7. The levels increased at Day 7 and then remained relatively constant until Day 20, after which they declined to reach typical adult male levels. Serum irI alpha levels were significantly lower in males than females from Days 25-40. There was a significant decrease in serum irI alpha 24 h after castration at all ages studied. Serum FSH levels in males were low until Day 20, increased at Day 25, and thereafter remained relatively unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation and thermal stability of the mite allergen DPT 12 in whole mite extracts.

Twelve whole mite extracts (WME) from seven sources were examined for their content of the allergen Dpt 12, protein content, and the inhibitory capacity in RAST by use of paper discs coupled with either WME or Dpt 12. Linear regression analysis demonstrated that the concentration of Dpt 12 determined either by single radial immunodiffusion or by RAST inhibition did not correlate with either the RAST-inhibition titer with use of discs coupled with WME or with protein content, suggesting that Dpt 12 content does not reflect the overall potency of WMEs. However, statistically significant correlations were obtained between Dpt 12 content and whole mite-RAST inhibition titers if extracts from the same manufacturer were examined or if data obtained from extracts containing large Dpt 12 to protein concentrations (greater than 25%) were excluded from the analysis. In contrast, statistically significant correlations between protein concentration and WME-RAST inhibition titers (p = 0.00037) and between Dpt 12 content and Dpt 12 RAST-inhibition titers (p = 0.00001) were found. Thermal stability studies demonstrated that Dpt 12 per se and WMEs were stable at 4 degrees C for up to 3 mo. Storage at 23 degrees C for 3 mo, however, resulted in partial loss of both Dpt 12 and whole-mite activity. Substantial losses occurred at 36 degrees C for both 1-month and 3-month incubation periods. Esterase, esterase lipase, and alkaline phosphatase were found in three WMEs studied. Dpt 12 was biochemically unrelated to these enzymes.

Synthesis of small proteoglycans substituted with keratan sulfate by rabbit articular chondrocytes.

35S-Labeled proteoglycans produced by chondrocytes from immature and mature rabbits were fractionated on associative CsCl gradients. In all cultures, greater than 85% of the incorporated radioactivity was present in the A1 fraction (rho 1.60) as chondroitin sulfate/keratin sulfate-substituted aggregating proteoglycan monomer; the remainder was present in small proteoglycans in the A2, A3, and A4 fractions of low buoyant densities (rho 1.53, 1.45, 1.37, respectively). Detailed glycosaminoglycan analysis of the A2, A3, and A4 fractions showed dermatan sulfate-rich species were present throughout. However, in both immature and mature cultures, 30-45% of the glycosaminoglycans in the A3/A4 combined fractions were present as keratan sulfate, as shown by insensitivity to digestion with chondroitinase ABC, specific digestion with endo-beta-galactosidase, and reactivity with antibody 5D4. Immature and mature chondrocytes synthesized very similar amounts of the low buoyant density keratan sulfate proteoglycan on a per cell basis. Moreover, 51 and 37% of the total keratan sulfate produced by immature and mature chondrocytes, respectively, were present in the low buoyant density proteoglycan. Pulse-chase experiments indicated that the low buoyant density keratan sulfate was not derived from the large aggregating proteoglycan by proteolysis in the extracellular space. The small keratan sulfate proteoglycans appear to be present as a species distinct from the small dermatan sulfate proteoglycans in these cultures in that they can be separated on Q-Sepharose chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The apparent size (40-60 kDa), composition, and heterogeneity of the keratan sulfate proteoglycans suggest that they may be related to the small keratan sulfate proteoglycans of cornea.

Immunochemical and enzymatic analyses of extracts of the house dust mite Dermatophagoides pteronyssinus.

The allergenicity and enzyme content of extracts of Dermatophagoides pteronyssinus whole mite, cuticle (CUT), and spent-growth medium (SGM) used in its culture have been examined. Both direct RAST binding and RAST-inhibition studies demonstrated that the whole mite extract was approximately threefold more potent than either the CUT or SGM extracts. Crossed immunoelectrophoresis and crossed radioimmunoelectrophoresis demonstrated that whole mite extracts contained 36 antigens of which nine were judged to be allergens (Dpt 1, 3, 4, 7, 8, 12, 17, 22, and 31). In contrast, extracts of CUT and SGM both contained 15 mite antigens of which five were judged to be allergens (Dpt 4, 8, 12, 17, and 22). Enzyme studies demonstrated that whole mite extracts from various sources contained esterases, phosphatases, aminopeptidases, and glycosidases. Both the CUT and SGM extracts contained a similar spectrum of enzymes, although the glycosidases were present at relatively low levels. Combined crossed immunoelectrophoresis and enzymic studies identified three antigens (Dpt 6, 13, and 24) with esterase activity, one antigen (Dpt 27) with beta-glucuronidase activity, and one antigen (Dpt 14) with acid phosphatase activity. Thus far, none of these enzymes has been demonstrated to be allergenic. Both enzymic and immunochemical studies suggested that not all mite allergens are of an excretory/secretory origin, but some (e.g., Dpt 1, 3, 4, 7, and 31) are derived from the whole mite per se.

Vaccine prophylaxis of Q fever. A follow-up study of the efficacy of Q-Vax (CSL) 1985-1990.

OBJECTIVES: To examine the efficacy of various batches of a formalin-inactivated whole cell Coxiella burnetti vaccine (Henzerling strain, Phase 1 [Q-Vax, CSL]) in the prevention of Q fever among abattoir workers. DESIGN AND SETTING: The study was a retrospective cohort survey of all employees at three South Australian abattoirs to determine the incidence of Q fever among vaccinated and unvaccinated employees during the period 1985 to 1990. RESULTS: There were two cases of Q fever among 2555 vaccinated employees of the three abattoirs, compared with 55 cases among 1365 unvaccinated employees. The two Q fever cases in vaccinated employees were within a few days of vaccination, before immunity had developed, and represented a coincidence of natural infection and vaccination. Protective efficacy was 100%, even with a batch of Q-Vax containing 20 micrograms/dose rather than the standard dose of 30 micrograms/dose. CONCLUSIONS: Vaccination was effective for at least five years, although it was uncertain whether this was due to the vaccine per se or to a combination of vaccine immunity reinforced by periodic natural exposure.

Molecular forms of gonadotropin-releasing hormone associated peptide (GAP): changes within the rat hypothalamus and release from hypothalamic cells in vitro.

We have developed RIAs using antisera directed against the cryptic peptide of the GnRH precursor (termed GnRH-associated peptide, GAP) and have used these together with a GnRH assay to characterize proGnRH-derived peptides in rat hypothalamic extracts. On Sephadex chromatography we have identified three molecular forms of GAP-like immunoreactivity (GAP-LI), in addition to the GnRH decapeptide. The largest of these forms is an 8.0-kilodalton (kD) GAP-LI which appears to be the complete proGnRH peptide. The second is a 6.5-kD GAP-LI, and is similar to the complete cryptic peptide (i.e. proGnRH14-69 or GAP1.56). The third peptide is a 2.5 kD C-terminal fragment of the cryptic peptide, representing a processed form of GAP. In whole hypothalamic extracts from normal rats the 8.0-kD form was the major form, comprising 60-70% of the total GAP-LI. All three forms were present in three distinct areas of the rat hypothalamus, namely median eminence (ME), anterior and mid-hypothalamus. However in the ME the proportion of 8.0-kD GAP-LI was significantly reduced and the proportion of 6.5-kD GAP-LI significantly increased compared to anterior and mid-hypothalamic samples (p less than 0.05). In whole hypothalamic extracts from pregnant and lactating rats the total content of proGnRH-derived peptides was reduced but the relative proportions of these peptides were not significantly changed from normal female rats. However, in postlactating rats, 2 weeks after removal of pups, the total levels of GAP-LI were unchanged compared to normals, but the percentage of 8.0-kD GAP-LI was significantly decreased and the percentage of 2.5-kD GAP-LI significantly increased compared to normals (p less than 0.05), suggesting that proGnRH may undergo additional processing dependent on physiological condition. In fetal and neonatal rats the proportion of the 6.5-kD peptide was increased and that of the 8.0-kD peptide decreased compared to adults, and this change became less significant with increasing age. In ovariectomized rats the proportion of 6.5-kD GAP-LI was increased and that of 8.0-kD GAP-LI decreased; this change was partially reversed with steroid treatment. Both the 6.5 and 2.5-kD forms were released by high K+ stimulation of neonatal hypothalamic cells in culture. These results indicate that there is differential processing of the proGnRH precursor within the hypothalamus and in altered physiological states.

Nonsteroidal signals originating in the gonads.

The discovery of the various peptide factors in the gonads followed different paths. A number of factors were specifically searched for because of physiological experiments that predicted that an activity from the gonads was necessary to explain phenomena. Such was the case for gonadal steroids and for such peptide factors as inhibin, MIS, OMI, FRP, seminal plasma inhibin, relaxin, PA factor and other proteases, and ABP. In the process other factors such as activin and follistatin were serendipitously discovered. A second group of factors was discovered because in vitro experiments of various combinations of gonadal cell types failed to replicate in vivo findings, suggesting missing signals. Such substances are the panoply of growth factors aiding in differentiation and growth promotion and inhibition: LS and LI, P-Mod-S, clusterin, and various components of the ECM. Finally, and most recently, another set of peptides has been identified because immunological or molecular probes have been used to search gonadal tissue for factors originally discovered elsewhere; these include POMC, GnRH-like peptide, oxytocin, AVP, angiotensin, ANF, CRF, neural peptides, and c-mos. Our understanding of the relationship of most of these peptides to the local signals necessary for gonadal function is still very elementary. Clearly some like relaxin and inhibin function as important hormones, and ABP, for example, probably functions importantly in transporting testosterone down the tubule. Most local paracrine or autocrine peptide signals appear to act in relationship to gonadotropin levels probably in local differentiation in the process of gamete maturation, but this is only conjecture at this point. No experimental verification that any of these factors is involved in follicle selection for recruitment or for atresia is yet available. For many of the factors local receptors have not yet been identified. The richness of the variety of peptides in the gonads suggests that microanalysis of cell-cell signaling would be rewarding, but at the time of this writing such investigations are not yet possible.

Changes in serum immunoreactive inhibin-alpha during photoperiod-induced testicular regression and recrudescence in the golden hamster.

Serum immunoreactive inhibin-alpha (irI alpha), FSH, LH, and testosterone (T) were measured in male golden hamsters during short-day-induced testicular regression and during testicular recrudescence following the transfer from short to long days. Serum FSH levels were maximally suppressed within 2 wk of transfer to short days. In contrast to FSH, irI alpha levels were not fully reduced until after 6 wk of exposure to short days, closely paralleling the timing of testicular regression. LH and T levels were also reduced within two 2k, with maximal suppression observed between 6 and 8 wk. Conversely, when males with regressed testes were transferred to long days, serum FSH rose to peak (25 ng/ml) levels by 3 wk and then declined to usual long-day levels. In contrast, serum irI alpha levels rose gradually, reaching adult long-day levels following 10 wk of exposure. Serum LH and T levels rose to peak levels between 5 and 8 wk before declining to adult levels. FSH, LH, and irI alpha levels were also measured after castration in male hamsters maintained on long or short days. Twenty-four hours after castration, levels of irI alpha were reduced in long-day males to levels comparable to those observed in castrated short-day males. Serum irI alpha levels respond slowly to abrupt changes in FSH levels after transfer to either long or short days, suggesting that testicular irI alpha secretion may not be directly and immediately influenced by circulating FSH levels in the hamster.(ABSTRACT TRUNCATED AT 250 WORDS)