The relative proportion of the circulating luteinizing hormone isoforms in goats during follicular phase (pre-ovulatory peak; F) and anestrus (A) was investigated. Estrus was synchronized in six goats with a prostaglandin analogue. After estrus was detected, blood samples were taken at 1 h intervals for 24 h. Four anestrous goats received 100 microg i.v. of GnRH and blood samples were collected every 15 min for 5 h. Samples with the greatest LH concentration in follicular phase and after GnRH administration (anestrus) were analyzed by chromatofocusing and eluted with a pH gradient from 10.5 to 3.5. For quantification purposes eluted LH was grouped into basic (pH> or =7.5), neutral (pH 7.4-6.5) and acidic isoforms (pH< or =6.4) as well as by pH unit. In both physiological conditions (PC), basic and acidic isoforms were greater than the neutral. With this grouping criteria, there was an interaction between PC and pH group, with the proportion of neutral isoforms being greater (p<0.05) in A (12.0+/-0.8%) as compared with F (5+/-2%). Analysis by pH unit showed a very basic group of eluted isoforms (pH> or =10), which amounted to a percentage of 6.0+/-0.4% of the total observed during A, and 3+/-1% during F (p<0.05). Predominant isoforms in A eluted in the pH range 9.99-9.0 (42+/-3%) as compared to 7+/-3% (p<0.01) in that pH range in F. In contrast, the predominant isoforms in F eluted in the pH range 8.99-8.0, representing 55+/-8%, while in A the proportion was 11+/-2% (p<0.01). Isoforms eluted at the pH range 7.9-7 represented a significantly greater proportion during A (5.0+/-0.6%) as compared with F (3+/-1%). This is the first report on goat LH circulating isoforms. During A the LH isoforms secreted by the pituitary are more basic than during F.