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The effects were studied of varying the frequency, width and amplitude of pulses of gonadotrophin releasing hormone (GnRH) on the release of LH from anterior pituitary cells. Dispersed sheep cells supported in Sephadex were perifused with medium for 10 h and stimulated with different constant pulse patterns of GnRH. The timing of release of LH was measured by radioimmunoassay of the effluent fractions. Pulses of GnRH ranging in duration from 2 min every 8 min to 16 min every 128 min, and in concentration from 1·7 pmol/l to 250 nmol/l were applied to the cells, as well as continuous stimulation. Comparisons of differences between LH release patterns among samples of the same preparation of cells were used to demonstrate the effects of different GnRH stimulatory regimes. It was concluded that (1) the frequency of GnRH stimulation was important to the nature of LH release (periods shorter than about 16 min between pulses reduced LH output and caused faster desensitization of response), (2) the pulse width of GnRH input was important (the rising edge of the pulse produced greater LH output per unit of GnRH input than did continued application of GnRH within a pulse and wider pulses combined with shorter periods reduced LH output) and (3) over a threshold value of 5–10 nmol GnRH/1 pulse amplitude had little further influence on LH output or rate of desensitization in dispersed cells. These findings reinforce the hypothesis that the rising edge of the GnRH pulse is the major stimulant to LH release.

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