Kinetics and disposition of picumeterol in animals

1. The pharmacokinetics and disposition of picumeterol, a novel beta 2 receptor agonist agent, have been studied in the rat and dog following administration by inhalation, intravenous and oral routes at various dose levels. 2. Picumeterol was found to be transferred across the lung of the rat and dog following inhalation dosage. After i.v. dosage picumeterol was eliminated from plasma with a half-life of about 1 h in the rat and about 2 h in the dog. Plasma clearance in the rat was about twice liver blood flow and the plasma levels of picumeterol were low after oral administration. 3. Following instillation of 14C-picumeterol to the trachea of isolated respiring rat lung preparations radioactivity was transferred from the airways to perfusion media as unchanged drug within 2 min. After 2 h perfusion, no metabolites were detected in the recirculation perfusate or lung. 4. Picumeterol was extensively metabolized in vivo in the rat (about 95%) and dog (about 90%) and in vitro in microsomal preparations of rat, dog and human liver. O-dealkylation and beta-oxidation are important as routes of metabolism. 5. Radioactivity was largely excreted in the urine of the rat and dog (> 50% of dose), as metabolites, following i.v. administration. There was some excretion of radioactivity in dog bile. Extensive first-pass metabolism was found after oral administration in the rat.

A dominant T cell receptor beta-chain in response to a short ragweed allergen, Amb a 5

HLA-DR alpha, beta 1 *1501 (and the closely related DR alpha, beta 1 *1502) heterodimers are the primary class II MHC restriction elements controlling T cell responses to a ragweed pollen allergen, Amb a 5 (M(r) = 5000). Using a novel, quantitative, competitive PCR (QC-PCR) assay and a TCR beta-gene internal standard (IS), we have examined the TCR beta-gene use in Amb a 5-specific T cells. Multiple TCR V beta (and V alpha) genes were found in polyclonal T cell lines from two unrelated subjects, and 30% of the cells were stained positive for V beta 5.2/5.3 as judged by a flow cytometry analysis. An Amb a 5-specific Th2 clone (AP1.2) was found to express V beta 5.2 (and V alpha 8) and to have a unique V-D-J junctional region sequence. To determine the relative frequency of clone AP1.2 beta-gene expression in the polyclonal T cell lines and in the PBMC using a QC-PCR assay, we first created a TCR IS by duplicating the J beta 1.5 gene segment of the AP1.2 beta-gene. A QC-PCR assay was performed using the modified AP1.2 beta-gene as a competitor and a V beta 5.2 or a D beta-specific primer, each paired with a C beta primer. Results showed the presence of 30% of AP1.2 beta transcripts in the polyclonal T cell lines, but no detectable amplified products were found in the total RNAs (200 ng) of autologous PBMC. These findings were confirmed by sequencing independent clones of PCR-amplified V beta 5.2-C beta fragments (from two unrelated subjects) from each cell line, which suggested that the frequency of the clone AP1.2 beta sequence is quite low in the PBMC but is dominant in polyclonal Amb a 5-specific cell lines.

A dominant T cell receptor beta-chain in response to a short ragweed allergen, Amb a 5

HLA-DR alpha, beta 1 *1501 (and the closely related DR alpha, beta 1 *1502) heterodimers are the primary class II MHC restriction elements controlling T cell responses to a ragweed pollen allergen, Amb a 5 (M(r) = 5000). Using a novel, quantitative, competitive PCR (QC-PCR) assay and a TCR beta-gene internal standard (IS), we have examined the TCR beta-gene use in Amb a 5-specific T cells. Multiple TCR V beta (and V alpha) genes were found in polyclonal T cell lines from two unrelated subjects, and 30% of the cells were stained positive for V beta 5.2/5.3 as judged by a flow cytometry analysis. An Amb a 5-specific Th2 clone (AP1.2) was found to express V beta 5.2 (and V alpha 8) and to have a unique V-D-J junctional region sequence. To determine the relative frequency of clone AP1.2 beta-gene expression in the polyclonal T cell lines and in the PBMC using a QC-PCR assay, we first created a TCR IS by duplicating the J beta 1.5 gene segment of the AP1.2 beta-gene. A QC-PCR assay was performed using the modified AP1.2 beta-gene as a competitor and a V beta 5.2 or a D beta-specific primer, each paired with a C beta primer. Results showed the presence of 30% of AP1.2 beta transcripts in the polyclonal T cell lines, but no detectable amplified products were found in the total RNAs (200 ng) of autologous PBMC. These findings were confirmed by sequencing independent clones of PCR-amplified V beta 5.2-C beta fragments (from two unrelated subjects) from each cell line, which suggested that the frequency of the clone AP1.2 beta sequence is quite low in the PBMC but is dominant in polyclonal Amb a 5-specific cell lines.

Analysis of the New Zealand Black contribution to lupus-like renal disease. Multiple genes that operate in a threshold manner

F1 progeny of New Zealand Black (NZB) and New Zealand White (NZW) mice spontaneously develop an autoimmune process remarkably similar to human systemic lupus erythematosus. Previous studies have implicated major genetic contributions from the NZW MHC and from a dominant NZB gene on chromosome 4. To identify additional NZB contributions to lupus-like disease, (NZB x SM/J)F1 x NZW backcross mice were followed for the development of severe renal disease and were comprehensively genotyped. Despite a 50% incidence of disease, significant associations between the presence of the NZB genotype and disease were noted on chromosomes 1, 4, 7, 10, 13, and 19. The data indicated that multiple NZB genes, in different combinations, contribute to severe renal disease, and that no single gene is required. To further investigate this NZB contribution, NZB x SM/J (NXSM) recombinant inbred (RI) strains were crossed with NZW mice, and F1 progeny were analyzed for the presence of lupus-like renal disease. Interestingly, nearly all of the (RI x NZW)F1 cohorts studied expressed some level of disease. Five RI strains generated a high incidence of disease, similar to (NZB x NZW)F1 mice, and nearly one-half of the cohorts developed disease at intermediate levels. Only two cohorts demonstrated very little disease, supporting the conclusion that multiple genes are capable of disease induction. Experiments correlating the genotypes of these RI strains with their ability to generate disease revealed that none of the disease-associated loci defined by the backcross analysis were present in all five RI strains that generated disease at high levels. Overall, both the backcross data and RI analysis provide additional support for the genetic complexity of lupus nephritis and uphold the conclusion that heterogeneous combinations of contributing NZB genes seem to operate in a threshold manner to generate the disease phenotype.

Analysis of the New Zealand Black contribution to lupus-like renal disease. Multiple genes that operate in a threshold manner

F1 progeny of New Zealand Black (NZB) and New Zealand White (NZW) mice spontaneously develop an autoimmune process remarkably similar to human systemic lupus erythematosus. Previous studies have implicated major genetic contributions from the NZW MHC and from a dominant NZB gene on chromosome 4. To identify additional NZB contributions to lupus-like disease, (NZB x SM/J)F1 x NZW backcross mice were followed for the development of severe renal disease and were comprehensively genotyped. Despite a 50% incidence of disease, significant associations between the presence of the NZB genotype and disease were noted on chromosomes 1, 4, 7, 10, 13, and 19. The data indicated that multiple NZB genes, in different combinations, contribute to severe renal disease, and that no single gene is required. To further investigate this NZB contribution, NZB x SM/J (NXSM) recombinant inbred (RI) strains were crossed with NZW mice, and F1 progeny were analyzed for the presence of lupus-like renal disease. Interestingly, nearly all of the (RI x NZW)F1 cohorts studied expressed some level of disease. Five RI strains generated a high incidence of disease, similar to (NZB x NZW)F1 mice, and nearly one-half of the cohorts developed disease at intermediate levels. Only two cohorts demonstrated very little disease, supporting the conclusion that multiple genes are capable of disease induction. Experiments correlating the genotypes of these RI strains with their ability to generate disease revealed that none of the disease-associated loci defined by the backcross analysis were present in all five RI strains that generated disease at high levels. Overall, both the backcross data and RI analysis provide additional support for the genetic complexity of lupus nephritis and uphold the conclusion that heterogeneous combinations of contributing NZB genes seem to operate in a threshold manner to generate the disease phenotype.

CART: a conserved antigen receptor transmembrane motif

We have compared the transmembrane sequences of 72 vertebrate antigen receptor (mIg and TCR) polypeptides. This allowed us to identify a Conserved Antigen Receptor Transmembrane (CART) motif which is present in all antigen receptor transmembrane domains from species as far removed as cartilaginous fish. Most of the amino acids in the CART motif are polar or aromatic and may interact with other proteins in the lipid environment. In addition, modeling the antigen receptor transmembrane domain in an alpha helical conformation places the CART residues on one face of the alpha helix. Thus, the CART motif may encode a structural unit which plays a role in the assembly and/or the signaling properties of lymphocyte antigen receptors. We speculate on the potential role of the CART motifs in lymphocyte signaling.

The processing of human ballistic movements explored by stimulation over the cortex

1. When seated human subjects abducted one arm rapidly in response to a tone there was successively a burst of electromyographic (EMG) activity in the deltoid and latissimus dorsi muscles followed by another burst in the deltoid muscle. This triphasic pattern is typical of a ballistic 'focal movement'. There were also bursts of EMG activity in the contralateral latissimus dorsi, pectoralis major and abdominal muscles, which were assumed to be 'associated postural adjustments'. The same bilateral pattern of muscle activity occurred in a deafferented subject. 2. When subjects abducted the left arm rapidly, magnetic stimulation over the left motor cortex delayed the onset of the EMG burst in the right latissimus dorsi relative to the initial burst in the left deltoid. When subjects abducted the right arm rapidly, magnetic stimulation over the left motor cortex delayed the onset of the initial EMG burst in the right deltoid relative to the burst in the left latissimus. In each case, the delay of an EMG burst was greatest (about 80 ms) when the stimulus was given just before the burst was expected to occur. The inhibition of voluntary movements by transcranial stimulation was not associated with a reduction in the excitability of spinal motoneurons. 3. We conclude that focal ballistic movements and their associated postural adjustments are generated in exactly the same way. We postulate that these movements are preprogrammed, held in a memory until the 'go' signal and then released through both motor cortices to spinal motoneurons.

An analysis of sequence variation in the beta chain framework and complementarity determining regions of an allo-reactive T cell receptor

Current models of T cell receptor (TCR) structure are generally based on the homology observed between the TCR and the immunoglobulins. Furthermore, these models have predicted the locations of framework and complementarity determining regions within the alpha- and beta-chain variable regions. In order to test the validity of these models, we have generated a series of mutations within the V beta domain of an allo-reactive TCR and determined their effect on antigen recognition.

Genetic analysis of the NZB contribution to lupus-like autoimmune disease in (NZB x NZW)F1 mice

Lupus-like autoimmunity in (NZB x NZW)F1 mice is frequently marked by the development of a severe and fatal renal disease. Genes from both NZB and NZW parents are required for the full expression of disease. We applied a mapping technique based on polymorphism in simple sequence repeats to the analysis of (NZB x NZW)F1 x NZW backcross mice to determine the NZB genetic contribution to disease. The results show that a single NZB locus or tightly linked group of loci on the distal part of chromosome 4 provides the strongest association with renal disease and death. This locus, designated here as nba-1 (New Zealand Black autoimmunity), lies distal to the locus elp-1, 60-70 centimorgans from the centromere. It is of interest that a gene encoding a receptor for tumor necrosis factor maps to the vicinity of this disease-associated gene.

Disposition of salmeterol xinafoate in laboratory animals and humans

The disposition of [14C]salmeterol xinafoate, a new inhaled beta 2-adrenoceptor agonist with both bronchodilator and antiinflammatory activity, has been studied in laboratory animals and humans following intravenous and oral administration. [14C]Salmeterol was rapidly absorbed in animal species and humans with Cmax observed within 2 hr. Cmax was similar for normalized oral dose level in mice, rats, and rabbits. In dogs, Cmax was higher and reflected the greater oral bioavailability in this species. The plasma t1/2, after intravenous administration, was 5 hr in rats and 2 hr in dogs. The volume of distribution of salmeterol was significantly greater than total body water in both rats (40 liters/kg) and dogs (6 liters/kg) and indicated high tissue uptake of the compound. Plasma clearance was high in rats (95 ml/min/kg) and dogs (30 ml/min/kg). Radioactive drug-related material was widely distributed throughout body tissues in rats. The highest concentrations were present in kidney, liver, gastrointestinal tract, pituitary, lung, heart, and bone marrow. Transfer of radioactive drug-related material across the placental barrier or into milk, studied in rats, was low. In all species the majority of an oral or intravenous dose (55-75%) was excreted in feces. Biliary excretion in rats and dogs accounted for 53% (0-27 hr) and 40% (0-8 hr) of an oral dose, respectively, indicating good absorption across the gastrointestinal tract. Enterohepatic circulation was significant in rats. Salmeterol was cleared predominantly by metabolism in animals and humans.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of morphological modifications of day 6.5 horse embryos after cryopreservation: differential effects on inner cell mass and trophoblast cells

Sixteen embryos were recovered nonsurgically at day 6.5 after induced ovulation from Welsh pony mares and were evaluated for cellular changes that occur because of exposure to the cryoprotectant with or without the freeze and thaw process. Day 6.5 horse embryos were either (i) frozen and thawed using glycerol as cryoprotectant (n = 6), (ii) given only the glycerol treatment (n = 5), or (iii) washed in phosphate-buffered saline (PBS) the same number of times as in the glycerol treatment (n = 5). After treatments, embryos were incubated in Minimum Essential Medium (MEM), supplemented with BSA, glutamine, antibiotics and buffered with Hepes, for 1 h for one embryo per group and for 6 h for the others. After histological fixation, embryos were serially sectioned. On observation by light microscopy, the total numbers of interphasic, mitotic and pycnotic nuclei of each embryo were counted. Electron microscopy was used to evaluate the damage to the fine structure of intracellular organelles. The proportion of mitotic cells did not differ among groups (control: 2.3%; glycerol-treated: 1.8%; frozen-thawed: 1.3%). There were significant differences in the proportion of pycnotic cells both between control (12.8% +/- 5.6) and glycerol-treated embryos (39.4% +/- 15.9) (P < 0.05) and between control and frozen-thawed embryos (42.2% +/- 14.9) (P < 0.001), but no difference was found between treated embryos (glycerol-treated and frozen-thawed embryos). Degenerated cells were not localized in the same place in each embryo and no ultrastructural alteration was uniformly observed among every embryo of each group, but inner cell mass (ICM) cells were affected most by treatments (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital cysts of the iris stroma

We managed three cases of congenital iris stromal cysts and compared them with 22 cases in the published reports to delineate the clinical features of this condition and determine the best treatment. Our first patient, a 5-month-old girl, had injection of a cyst with trichloroacetic acid, but developed a cataract and endothelial damage to the cornea and the eye was eventually enucleated. Our second patient, a 9-week-old girl, was treated with repeated xenon photocoagulation, drainage of the cyst, and cryotherapy, but required enucleation of the eye. Our third patient, a 5-month-old girl, had excision of the cyst by sector iridectomy with preservation of vision and no recurrence two years later. Our results suggest that complete surgical excision is a superior method of treatment for congenital cysts of the iris stroma.

Induction of ovulation and superovulation in mares using equine LH and FSH separated by hydrophobic interaction chromatography

Pharmacological control of reproduction in mares requires the use of equine gonadotrophins to avoid induced immunological resistance. Crude equine gonadotrophins (CEG) have been used but the presence of equine luteinizing hormone (eLH) and follicle-stimulating hormone (eFSH) in CEG has led to disappointing results in superovulation studies. Separation of eLH and eFSH activities from CEG is necessary to overcome this problem. The hydrophobic properties of the two hormones were sufficiently different to permit their separation by hydrophobic interaction chromatography (HIC) on a phenyl Sepharose matrix. Good yields of separate FSH and LH fractions were readily obtained by stepwise elution and the method was adapted for large scale preparations of enriched fractions of eLH and eFSH. Two experiments were performed in vivo to evaluate the biological activity of the HIC fractions. Experiment 1 showed that biological activity of the LH fraction in inducing ovulation of preovulatory follicles was similar to that obtained with CEG, indicating that LH bioactivity was not altered by HIC. Experiment 2 demonstrated that biological activity of the FSH fraction was identical (as far as rate of ovulation was concerned) to that of CEG in superovulating mares, indicating that FSH activity was also not altered by HIC. Although we have not obtained better results with the separate equine gonadotrophins than with CEG, it is potentially advantageous to use preparations with single activity to obtain a controlled balance of FSH and LH activity. The HIC technique was chosen because it could easily be scaled up to provide the large amounts of the separate hormones needed for the treatment of a large number of mares.

Aberrant induction of T cell tolerance in B cell suppressed mice

Self-tolerance is the process by which the T cell repertoire develops without expressing self-reactive specificities. The mechanisms which functionally eliminate self-reactive T cells are clonal deletion and clonal inactivation, and both of these phenomena have been studied in T cell populations reactive to endogenous superantigens that are encoded by endogenous mouse mammary tumor proviruses (Mtv). The studies described here demonstrate that the kinetics of Etc-1 (encoded by the Mtv-9 open reading frame gene)-mediated deletion are much slower than that seen for Mls 1a (encoded by the Mtv-7 open reading frame), and that Etc-1-reactive T cells are present in the periphery up to 2 wk after birth. The deletion of peripheral Etc-1-reactive T cells late in ontogeny indicates an efficient mechanism of peripheral clonal deletion in these animals. The clonal deletion of Etc-1-reactive cells is abrogated in B cell-suppressed animals; however, clonal elimination of peripheral V beta 5+ or V beta 11+ (Etc-1 reactive) T cells can be induced when these mice are allowed to recover their B cell population after cessation of anti-mu treatment. Finally, we establish that peripheral Etc-1-reactive V beta 11+/CD4+ T cells remaining in B cell-suppressed and recovering animals are markedly less responsive to stimulation through the TCR than are control T cells. These data support the idea that peripheral self-reactive T cells can be rendered tolerant by two mechanisms which may be temporally related. This model suggests that clonal hyporesponsiveness may be followed by clonal deletion.

Aberrant induction of T cell tolerance in B cell suppressed mice

Self-tolerance is the process by which the T cell repertoire develops without expressing self-reactive specificities. The mechanisms which functionally eliminate self-reactive T cells are clonal deletion and clonal inactivation, and both of these phenomena have been studied in T cell populations reactive to endogenous superantigens that are encoded by endogenous mouse mammary tumor proviruses (Mtv). The studies described here demonstrate that the kinetics of Etc-1 (encoded by the Mtv-9 open reading frame gene)-mediated deletion are much slower than that seen for Mls 1a (encoded by the Mtv-7 open reading frame), and that Etc-1-reactive T cells are present in the periphery up to 2 wk after birth. The deletion of peripheral Etc-1-reactive T cells late in ontogeny indicates an efficient mechanism of peripheral clonal deletion in these animals. The clonal deletion of Etc-1-reactive cells is abrogated in B cell-suppressed animals; however, clonal elimination of peripheral V beta 5+ or V beta 11+ (Etc-1 reactive) T cells can be induced when these mice are allowed to recover their B cell population after cessation of anti-mu treatment. Finally, we establish that peripheral Etc-1-reactive V beta 11+/CD4+ T cells remaining in B cell-suppressed and recovering animals are markedly less responsive to stimulation through the TCR than are control T cells. These data support the idea that peripheral self-reactive T cells can be rendered tolerant by two mechanisms which may be temporally related. This model suggests that clonal hyporesponsiveness may be followed by clonal deletion.

Production of DNP-specific/class I MHC-restricted suppressor molecules is linked to the expression of T cell receptor alpha- and beta-chain genes

The hapten/class I MHC-specific soluble immunoregulatory molecules produced by CD8+T cells from dinitrobenzene sulfonate-primed mice express the binding specificity and serologic determinants of alpha/beta TCR. To examine the genes used to encode these soluble immunoregulatory molecules, we utilized a surface TCR expressing Ts hybridoma, which constitutively produces a DNP/Kd-specific regulatory molecule. Northern and Southern analyses indicated that MTs 79.1 cells use a V beta 8 and a V alpha 4 gene to encode the variable regions of the surface alpha/beta TCR. A panel of TCR- variants was generated by subjecting MTs 79.1 cells to gamma-irradiation. Twelve of the TCR- variants were chosen for detailed characterization. Northern blot analyses indicated the absence of the MTs 79.1 V alpha 4 chain transcript in five of the variants and the absence of the parental V beta 8 chain transcript in the other seven. Southern blot analyses demonstrated the deletion of the parental gene encoding the alpha- or beta-chain from the genome of the respective mutant. None of the 12 TCR gene deletion mutants produced the parental suppressive activity. Expression of the parental TCR beta-chain gene in one of the beta-chain gene deletion mutants reconstituted the ability to produce this activity. As with the MTs 79.1 molecule, the regulatory molecule produced by the beta-chain gene transfectant was bound by and eluted from Sepharose columns coupled with either DNP or anti-V beta 8 antibodies. These results establish a strong linkage between the suppressor molecules produced by these Ts and TCR alpha- and beta-chain gene transcription.

Production of DNP-specific/class I MHC-restricted suppressor molecules is linked to the expression of T cell receptor alpha- and beta-chain genes

The hapten/class I MHC-specific soluble immunoregulatory molecules produced by CD8+T cells from dinitrobenzene sulfonate-primed mice express the binding specificity and serologic determinants of alpha/beta TCR. To examine the genes used to encode these soluble immunoregulatory molecules, we utilized a surface TCR expressing Ts hybridoma, which constitutively produces a DNP/Kd-specific regulatory molecule. Northern and Southern analyses indicated that MTs 79.1 cells use a V beta 8 and a V alpha 4 gene to encode the variable regions of the surface alpha/beta TCR. A panel of TCR- variants was generated by subjecting MTs 79.1 cells to gamma-irradiation. Twelve of the TCR- variants were chosen for detailed characterization. Northern blot analyses indicated the absence of the MTs 79.1 V alpha 4 chain transcript in five of the variants and the absence of the parental V beta 8 chain transcript in the other seven. Southern blot analyses demonstrated the deletion of the parental gene encoding the alpha- or beta-chain from the genome of the respective mutant. None of the 12 TCR gene deletion mutants produced the parental suppressive activity. Expression of the parental TCR beta-chain gene in one of the beta-chain gene deletion mutants reconstituted the ability to produce this activity. As with the MTs 79.1 molecule, the regulatory molecule produced by the beta-chain gene transfectant was bound by and eluted from Sepharose columns coupled with either DNP or anti-V beta 8 antibodies. These results establish a strong linkage between the suppressor molecules produced by these Ts and TCR alpha- and beta-chain gene transcription.

Ipsilateral fast corticospinal pathways do not account for recovery in stroke

We tested the hypothesis that in adult humans, recovery from stroke results from the emergence of ipsilateral, fast-conducting corticospinal pathways. In 10 patients recovering from stroke, the unaffected hemisphere was stimulated with an electromagnet and changes in the firing probability of single biceps motor units were used to derive postsynaptic potentials in single biceps motoneurons. Stimuli sufficient to excite the neurons of the fast-conducting corticospinal pathway (as shown by short-latency facilitation of contralateral biceps motoneurons) did not produce short-latency depolarization of ipsilateral biceps motoneurons. The hypothesis is therefore not supported.

The transcortical nature of the late reflex responses in human small hand muscle to digital nerve stimulation

The hypothesis that long-latency reflex activity in human small hand muscles in response to stimulation of digital nerves involves a transcortical pathway was tested by combining digital nerve stimulation and magnetic stimulation over the motor cortex in 12 studies on nine normal subjects. Postsynaptic events in human single first dorsal interosseous (FDI) motoneurones were derived from changes in the firing probability of voluntarily activated single motor units. Electromagnetic stimulation over the contralateral motor cortex resulted in a short-latency, brief facilitation of FDI motor units considered to be due to the activation of "fast" corticospinal neurones making monosynaptic projections to motoneurones. Stimulation of the digital nerves of the index finger produced a period of reduced firing probability (I1), a period of increased firing probability (E2) and a further period of reduced firing probability (I2) in FDI motor units. When the two stimuli were given separately and then together, timed so that the magnetic stimulus occurred at the predicted transit time of the E2 through the cortex, the facilitation of FDI motoneurones by the combined stimulation was often less than the algebraic sum of the facilitations from each stimulus alone. Thus, in contrast to the results of similar studies on the late response to muscle stretch, there is no confirmation that the E2 from digital nerve stimulation is due to a transcortical reflex.

Initiation of superovulation in mares 5 or 12 days after ovulation using equine pituitary extract with or without GnRH analogue

Cyclic mares were assigned to 1 of 3 treatments (n=15 per group): Group 1 received equine pituitary extract (EPE; 25 mg, i.m.) on Day 5 after ovulation; Group 2 received EPE on Day 12 after ovulation; while Group 3 received 3.3 mg of GnRH analogue (buserelin implant) on the day of ovulation and 25 mg, i.m. EPE on Day 12. Mares in each group were given 10 mg PGF2alpha on the first and second day of EPE treatment. The EPE treatment was continued daily until the first spontaneous ovulation, at which time 3,300 IU of human chorionic gonadotropin (hCG) were given to induce further ovulations. Mares in estrus with a >or=35 mm follicle were inseminated every other day with pooled semen from 2 stallions. Embryo recovery was attempted 7 days after the last ovulation. Follicular changes and embryo recovery during 15 estrous cycles prior to treatment were used as control data. During treatment, the number of follicles>or=25 mm was higher (P<0.05) for Day 5 than for Day 12 or control mares, but the number for Day-5 mares was similar (P>0.05) to that of mares treated with buserelin implants (Group 3). Initiation of EPE treatment on Day 5 resulted in a greater (P<0.05) number of ovulation (2.9) than on Day 12 (1.1) or in the control mares (1.3) but not in the buserelin-treated mares (1.8). The number of embryos recovered from mares in the Day 5 (1.2), Day 12 (1.0), buserelin (0.9) and control (0.9) groups was similar (P>0.05). The conclusions were 1) EPE initiated in early diestrus increased follicular development and ovulation and 2) treatment with GnRH analogue marginally improved response to EPE treatment.