We tested the hypothesis that hypotension occurred in older adults at the onset of orthostatic challenge as a result of vagal dysfunction. Responses of heart rate (HR) and mean arterial pressure (MAP) were compared between 10 healthy older and younger adults during onset and sustained lower body negative pressure (LBNP). A younger group was also assessed after blockade of the parasympathetic nervous system with the use of atropine or glycopyrrolate and after blockade of the beta(1)-adrenoceptor by use of metoprolol. Baseline HR (older vs. younger: 59 +/- 4 vs. 54 +/- 1 beats/min) and MAP (83 +/- 2 vs. 89 +/- 3 mmHg) were not significantly different between the groups. During -40 Torr, significant tachycardia occurred at the first HR response in the younger subjects without hypotension, whereas significant hypotension [change in MAP (DeltaMAP) -7 +/- 2 mmHg] was observed in the elderly without tachycardia. After the parasympathetic blockade, tachycardiac responses of younger subjects were diminished and associated with a significant hypotension at the onset of LBNP. However, MAP was not affected after the cardiac sympathetic blockade. We concluded that the elderly experienced orthostatic hypotension at the onset of orthostatic challenge because of a diminished HR response. However, an augmented vasoconstriction helped with the maintenance of their blood pressure during sustained LBNP.

Two cDNA clones (CRH1 and CRH2) homologous to animal calreticulin, a major calcium storage protein in the lumen of the endoplasmic reticulum, were isolated from an ovary cDNA library of barley through differential screening. The two clones differ in the 3' untranslated region and the 5' region that encodes a putative N-terminal signal sequence. CRH1 was mapped to the minus arm of chromosome 1. CRH2 was mapped to the minus arm of chromosome 2. The deduced amino acid sequences share 50 to 55% identity with animal calreticulins and exhibit the same three-zone characteristic. Recombinant protein stained blue with Stains-all and bound 45Ca2+ when transferred to nitrocellulose membranes. A native protein of approximately 55 kD was identified in ovary extract. Elevated gene expression was observed in ovaries 1 day after pollination and during early embryogenesis. CRH1 was expressed at a higher level than CRH2. These studies demonstrate the presence of calreticulin in plant cells and its developmental regulation in fertilization.

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