Pulsatile luteinizing hormone secretion in the rat: methodological aspects of cannulation route and sampling...

Abstract We have investigated some requirements for valid estimates of pulsatile luteinizing hormone (LH) secretion in the castrate male rat. The choice of cannulation route and the minimal sampling intensity required to produce stable, unbiased estimates of parameters of pulsatile LH secretion were examined. Castrate mature male Wistar rats with unilateral ligation of a carotid artery (an inevitable consequence of carotid artery cannulation) had a 47% reduction in mean LH levels (1.8 vs 3.4 ng/ml, P< 0.011) attributable to a 40% reduction in LH pulse frequency (6.2 vs 10.4 peaks/6 h P<0.006) without change in LH pulse amplitude or other parameters of pulsatile LH secretion. In another study, a range of sampling intensities were examined to derive estimates of pulsatile LH secretion. Parameter estimates derived from the most intensive regime (q10 min sampling for 6 h) were compared with estimates of pulsatile LH secretion parameters determined from less intensive derivative sub-series composed of either fixed sampling frequency, but variable total study duration (i.e. the first 1, 2, 3, 4 and 5 h at 10 min intervals), or a fixed total study duration but variable sampling frequency. LH pulse frequency (or its inverse, interpulse interval) was quite sensitive to sampling intensity whereas pulse amplitude, maximum, minimum and overall mean LH were estimated accurately at even relatively low sampling intensity (q20 min for one h duration). Lower frequency sampling (q20 min) gave marked underestimates of LH pulse frequency (4.9 vs 10.4 peaks/6 h, P<0.05) compared with q10min sampling over a 6h study. These results indicated that for stable and unbiased estimates of pulsatile LH secretion in the castrate mature male rat it is necessary (but may not be sufficient) to (1) avoid carotid artery cannulation and (2) undertake blood sampling at intervals of not more than 10 min for at least 3 h.