The pars tuberalis of the ewe: no effect of season or ovariectomy on the distribution, density or presence of immunoreactive cells

Abstract.

This study investigated whether season or long-term ovariectomy influence the presence, distribution and density of immunoreactive cells in the ovine pars tuberalis. Three groups of ewes were used: breeding season (BS; n=5), anoestrous (AS; n=8) and ovariectomised (OVX; n=4). Two rams were also investigated for possible sex-dependent differences. Employing standard immunocytochemical techniques, paraformaldehyde-fixed sagittal pars tuberalis and pars distalis sections were immunoreacted against luteinising hormone, luteinising hormone β-subunit, thyroid-stimulating hormone, prolactin, growth hormone, β-endorphin and adrenocorticotrophic hormone. Numerous gonadotrophs were detected in the anteroventral region of the pars tuberalis and there was no significant difference in the density (gonadotrophs/0.01 mm²; BS: 44±13, AS: 29±2, OVX: 27±4) or percentage of total cells (%; BS: 48±8, AS: 45±4, OVX: 49±2); the rams also appeared similar (27±2 gonadotrophs/0.01 mm²; 49±1%). In contrast, few gonadotrophs (less than 1%) were detected in the anterodorsal and posterior pars tuberalis regions. Apart from occasional thyrotrophs in the anteroventral pars tuberalis (less than 4%), no other pars distalis hormone-containing cells were detected in the pars tuberalis. This study demonstrates, therefore, that the anteroventral pars tuberalis represents an enriched population of immunoreactive gonadotrophs, whose number and distribution is similar in variable endocrine states. The protein phenotype(s) of cells in the other pars tuberalis regions remains undetermined.