Inhibitory effects of the neurotensin analogs Asp-NT and Asp-NT on mast cell secretion.

Pretreatment of isolated mast cells with analogs of neurotensin 8-13 (NT), in which the amino acids Leu or Ile are replaced with an aspartic acid (Asp-NT or Asp-NT), inhibits the secretion of histamine in response to NT. A 10 min pretreatment with either analog (10 μ M) inhibited NT-induced histamine release by 90% (Asp-NT) or by 98% (Asp-NT). At concentrations that are inhibitory, Asp-NT and Asp-NT alone elicit very little release (<5% at 10 μ M). In the continued presence of the analogs, the inhibitory effect lasts for more than 45 min; removal of the analogs resulted in restoration of sensitivity to NT within 10 min. Pretreatment with analog Asp-NT resulted in a 39% inhibition of stimulation by substance P and a 52% inhibition of stimulation by histaminereleasing peptide (HRP). In contrast, pretreatment with analog Asp-NT gave no inhibition of release by SP or HRP. Neither analog inhibited histamine release in response to bradykinin (BK), NT, compound 48/80 (48/80), the calcium ionophore A23187, or anti-IgE stimulation of passively sensitized mast cells. Although Asp-NT and Asp-NT differ slightly in regard to the peptides they inhibit, both probably act at a step early in the stimulus-secretion coupling sequence; most likely before the rise in the level of free intracellular calcium that has been shown to accompany secretion in mast cells. It is suggested that these analogs exert their inhibitory effect on NT by competing with NT for a binding site on the mast cell membrane. The limited number of peptides inhibited by these analogs suggest that not all basic peptides act at the same site to stimulate secretion. [ABSTRACT FROM AUTHOR]