In addition to those already mentioned, various other biogenic amine receptors are known to be affected by the ergot alkaloids of E+ tall fescue. For example, stimulation of a-2 adrenergic receptors by the alkaloids (Oliver et al., 1998) resulted in enhancement of blood platelet aggregation, which likely is involved in the coagulopathies and tissue necrosis (fescue foot) that occur with severe toxicity (Oliver, 1997, 2005). Stimulation of the dopamine-2 receptor (Larson et al., 1994, 1995) by ergot alkaloids found in E+ tall fescue is known to cause a decrease in prolactin secretion, which is linked to decreased milk secretion and agalactia in animals that graze E+ tall fescue (Strickland et al., 1993). Ergot alkaloids (i.e., ergine, ergovaline) also appear to interact with serotonin-2 receptors. Oliver and Abney (1989) and others (Dyer, 1993, 2000; Oliver et al., 1993; Vanhoutte and Luscher, 1986) have found that serotonin-induced contraction of vascular smooth muscle was associated with serotonergic-2 receptor activity. Serotonin is known to affect the hypothalamic satiety center, with increased levels resulting in suppression of appetite (Rossi-Fanelli and Cangiano, 1991), a possible mechanism by which ergot alkaloids might decrease feed intake. Support of alkaloid effects on neurotransmitter systems has been provided by Porter (1995) and Oliver et al. (2000b). Whereas Porter (1995) demonstrated that cattle grazing E+ tall fescue have increased serotonin metabolites in central nervous system tissues, Oliver et al. (2000b) showed increased tryptophan levels in sera of cattle grazing E+ tall fescue. This latter finding also is a condition that results in decreased feed intake (Smith, 1992; Porter, 1995; Meloche and Smith, 1995; Smith and Seddon, 1998).


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