Table 4. The production of 1-deoxysphingosine and 1-deoxysphinganine after X-ray irradiation.

X-ray dose (Gy)	Irradiation time (hr)	1-deoxysphingosine (pmol/mg)	1-deoxysphinganine (pmol/mg)
3	0	7.23±0.45	29.77±2.62
	12	7.25±0.56	31.70±2.14
	18	7.13±0.47	35.66±3.01*
	24	9.42±0.95*	38.86±3.21**
6	0	7.31±0.62	29.50±3.09
	12	7.94±0.46	29.99±2.41
	18	8.94±0.81	34.26±4.12
	24	11.27±0.91**	44.26±3.24***

Values are presented as mean±standard deviation (pmol/mg). ^*p<0.05, ^**p<0.01, and ^***p<0.001 compared to untreated normal human epidermal keratinocytes.