Dynamic characteristics of luteinizing hormone release from perifused XXXX anterior pituitary cells stimulated by combined pulsatile and continuous gonadotropin-releasing hormone.

@entity742 @entity1176
We aim to quantify and relate the dominant dynamic factors of @entity1176 signals and of the resultant patterns of LH release from pituitary cells. Using perifused @entity742 cells we have already shown that rising edges of @entity1176 pulses are major effectors of LH release and that a longer absence of signal between pulses improves response. This study reports the effects on LH release dynamics of continuous levels of @entity1176 with superimposed pulses and of slowing the important rising edge of the @entity1176 pulses. Low baseline @entity1176 perifusions at physiological levels (5-60 pM) reduced the response to hourly pulses of 850 pM @entity1176 . Continuous @entity1176 (420 pM), which initially yielded maximal LH release followed by desensitization, prevented extra stimulation by pulses of equal concentration, but 10-fold higher pulses gave additional LH output. After desensitization an hour's respite from stimulation resensitized cells to 420 pM pulses. Whereas continuous stimulation of cells with @entity1176 even at the very low level of 5-10 pM [ED50 = 58 +/- 6 (SE) pM] produced desensitization in 10-15 min, slowly rising @entity1176 (0.56-14 pM/min) caused increasing LH output with time. However, in comparison with square wave pulses, stimulatory signals consisting of slowly rising concentrations of @entity1176 produced peaks characterized by less total LH output and a changed shape. This was consistent with desensitization at low concentrations of @entity1176 reducing response to later increases in the level of stimulation. The mechanism for detecting @entity1176 signals and/or the mechanisms controlling release of LH were desensitized to constant @entity1176 at any concentration but retained a reduced sensitivity, or developed an additional release capacity, to increased levels of @entity1176 . Properties of four distinct types of LH release dynamics were described quantitatively and were shown to be controlled by different time constants in the @entity1176 pulse stimulation patterns.
