Retinoic acid is present in the postnatal rat olfactory organ and persists in vitamin A--depleted neural tissue

Abstract

Vitamin A (VA), all-trans-retinol (at-ROL), and its derivative, all-trans-retinoic acid (at-RA), are required for neuron development. The effects of these retinoids are dependent upon the nutritional status of the rat and tissue-specific dynamics of retinoid access and utilization. The purpose of this study was to determine the status of at-ROL and at-RA in the peripheral olfactory organ of postnatal rats fed a normal diet and rats fed a VA-deficient (VAD) diet. Extracted retinoids were analyzed by HPLC. Resolved sample peaks were identified by comparing their elution times and spectra with those of authentic standards. Mean at-RA and at-ROL concentrations of 23 pmol/g olfactory tissue and 0.13 nmol/g, respectively, were recovered from olfactory tissue. The ratio of at-RA:at-ROL in olfactory was approximately 2 times that in testis and 200 times that in liver. at-ROL was depleted from the liver and olfactory organ of rats fed a VAD diet from birth to 70 d of age. Surprisingly, at-RA was still present in olfactory tissue from these rats. At 90 d of age, the VAD rats were frankly deficient and at-RA was no longer detectable in olfactory tissue. The comparatively high ratio of at-RA:at-ROL in the peripheral olfactory organ and the persistence of at-RA in at-ROL-depleted tissues strongly suggests that maintenance of local stores of at-RA is functionally relevant in this tissue.

FIGURE 1

at-RA and at-ROL are present in the postnatal rat peripheral olfactory organ. (A) HPLC traces of separations of a mixture of authentic retinoid standards (upper trace) and postnatal rat olfactory tissue (lower trace). The vertical dotted black lines that pass through peak maxima at 15.1 and 15.6 min show the exact alignment of olfactory sample peaks with at-RA (peak 3) and at-ROL (peak 4) standard peaks, respectively. Retinoid standard peak 1 is 13-cis- RA, 2 is 9-cis-RA, and 5 is at-RAL. (B) The chromatogram of a second olfactory extract. The spectrum of the peak eluting at 15.1 min (solid trace, left inset) matches the spectrum of authentic at-RA (dashed trace, left inset). The spectrum of the peak eluting at 15.6 min (solid trace, right inset) matches the spectrum of authentic at-ROL (dashed trace, right inset). Axes of spectral trace insets here and in Figure 2 are labeled as follows: Norm on Y-axis refers to normalized milli-absorbance units; wavelength on X-axis is in nm.

FIGURE 2

Detection of at-RA and at-ROL in postnatal rat brain. Chromatographic traces showing separation of pooled retinoid standards (upper panel) and a rat brain extract (lower panel). The vertical dotted black lines that encompass peaks 2, 3, and 4 show the alignment of brain sample peaks with standard 9-cis-RA, at-RA, and at-ROL peaks, respectively. The inset below peak 3 shows overlaid sample (solid trace) and at-RA standard (dash-dot trace) spectra. The inset below peak 4 shows overlaid sample (solid trace) and at-ROL standard (dash-dot trace) spectra. Retinoid standard peak 1 is 13-cis-RA.